Integrated piezoelectric microelectromechanical ultrasound transducer (PMUT) on integrated circuit (IC) for fingerprint sensing

ABSTRACT

Microelectromechanical (MEMS) devices and associated methods are disclosed. Piezoelectric MEMS transducers (PMUTs) suitable for integration with complementary metal oxide semiconductor (CMOS) integrated circuit (IC), as well as PMUT arrays having high fill factor for fingerprint sensing, are described.

PRIORITY CLAIM

This patent application is a divisional application that claims priorityto U.S. patent application Ser. No. 15/853,396, filed Dec. 22, 2017,entitled “INTEGRATED PIEZOELECTRIC MICROELECTROMECHANICAL ULTRASOUNDTRANSDUCER (PMUT) ON INTEGRATED CIRCUIT (IC) FOR FINGERPRINT SENSING,”which patent application is a continuation-in-part application thatclaims priority to U.S. patent application Ser. No. 14/829,404, filedAug. 18, 2015, entitled “INTEGRATED PIEZOELECTRIC MICROELECTROMECHANICALULTRASOUND TRANSDUCER (PMUT) ON INTEGRATED CIRCUIT (IC) FOR FINGERPRINTSENSING,” which is continuation-in-part application of U.S. patentapplication Ser. No. 14/480,051, filed Sep. 8, 2014, entitled “ALUMINUMNITRIDE (AlN) DEVICES WITH INFRARED ABSORPTION STRUCTURAL LAYER,” whichis a non-provisional application of U.S. Provisional Patent ApplicationSer. No. 61/880,110, filed Sep. 19, 2013, entitled “ALUMINUM NITRIDE(AlN) DEVICES WITH IR ABSORPTION STRUCTURAL LAYER AND METHOD OFFABRICATING THE SAME,” and which is a continuation-in-part applicationthat claims priority to U.S. patent application Ser. No. 13/687,304,filed Nov. 28, 2012, entitled “MEMS DEVICE AND PROCESS FOR RF AND LOWRESISTANCE APPLICATIONS,” this patent application is acontinuation-in-part application that claims priority to U.S. patentapplication Ser. No. 14/453,326, filed Aug. 6, 2014, entitled“PIEZOELECTRIC ACOUSTIC RESONATOR BASED SENSOR,” this patent applicationis a non-provisional application of U.S. Provisional Patent ApplicationSer. No. 62/153,480, filed Apr. 27, 2015, entitled “INTEGRATED PMUT ONIC FOR FINGERPRINT SENSING.” The entirety of the aforementionedapplications is incorporated by reference herein.

TECHNICAL FIELD

The subject disclosure relates to microelectromechanical (MEMS) devices,to piezoelectric MEMS devices for fingerprint sensing, and moreparticularly to integrated piezoelectric MEMS transducers (PMUTs) onintegrated circuit (IC) for fingerprint sensing.

BACKGROUND

Microelectromechanical systems enable integration of bothmicroelectronic circuits and mechanical structures on a single chip ordevice, thereby significantly lowering fabrication costs and/or chipsize. For instance, compared with their bulk piezoelectric counterparts,MEMS ultrasound transducers (MUT) can have applications not possible inconventional bulk piezoelectric devices, e.g., medical imaging, such asintravascular guiding and diagnosis, fingerprint detection, etc. Forexample, traditional manufacturing methods are ineffective in creatingarea array interconnection and reduced transducer sizes.

However, MUT devices, as an alternative method for fingerprint detectiontypically require MUT devices to be manufactured in the resolution of atleast 300 dots per inch (dpi) or higher e.g., approximately 85micrometer (μm) pixel size. Conventional manufacturing process flows,e.g., with traditional polishing and sawing from bulk piezoelectricmaterials have not been able to achieve required resolutions, whereas acapacitive MUT (CMUT) linear array can provide such resolution. However,CMUT linear arrays are subject to skin condition and sensorcontamination, which can deteriorate the accuracy of fingerprintdetection devices employing CMUT linear arrays.

It is thus desired to provide integrated piezoelectric MEMS transducers(PMUTs) on integrated circuit (IC) for fingerprint sensing that improveupon these and other deficiencies. The above-described deficiencies aremerely intended to provide an overview of some of the problems ofconventional implementations, and are not intended to be exhaustive.Other problems with conventional implementations and techniques, andcorresponding benefits of the various aspects described herein, maybecome further apparent upon review of the following description.

SUMMARY

The following presents a simplified summary of the specification toprovide a basic understanding of some aspects of the specification. Thissummary is not an extensive overview of the specification. It isintended to neither identify key or critical elements of thespecification nor delineate any scope particular to any embodiments ofthe specification, or any scope of the claims. Its sole purpose is topresent some concepts of the specification in a simplified form as aprelude to the more detailed description that is presented later.

In a non-limiting example, an exemplary MEMS device can comprise a MEMSultrasound transducer (MUT) structure and a piezoelectric materialdisposed within the MEMS device comprising a piezoelectric MUT (PMUT)array of a fingerprint sensor adapted to sense a characteristic of afingerprint placed adjacent to the MUT structure. An exemplary MEMSdevice can further comprise a first metal conductive layer disposed onthe piezoelectric material and a plurality of metal electrodesconfigured to form electrical connections between the first metalconductive layer, the piezoelectric material, and a complementary metaloxide semiconductor (CMOS) structure, wherein the pMUT structure and theCMOS structure are vertically stacked.

In another non-limiting example, an exemplary MEMS device can comprise aCMOS device wafer associated with an integrated PMUT array of afingerprint sensor and having a plurality of cavities configured in anarray. An exemplary MEMS device can further comprise a first metalconductive layer disposed on the CMOS device wafer and over theplurality of cavities, a piezoelectric material disposed on the firstmetal conductive layer, and a second metal conductive layer, disposed onthe piezoelectric material, electrically coupling the second metalconductive layer and at least one CMOS device wafer electrode, andelectrically coupling the first metal conductive layer to at least oneother CMOS device wafer electrode, wherein the plurality of cavities,the piezoelectric material, the first metal conductive layer, and thesecond metal conductive layer are configured as a plurality of PMUTstructures.

In a further non-limiting example, exemplary methods are describeddirected to PMUTs suitable for integration with CMOS integrated circuits(ICs), as well as PMUT arrays having high fill factor for fingerprintsensing.

These and other embodiments are described in more detail below. Thefollowing description and the annexed drawings set forth certainillustrative aspects of the specification. These aspects are indicative,however, of but a few of the various ways in which the principles of thespecification may be employed. Other advantages and novel features ofthe specification will become apparent from the following detaileddescription of the specification when considered in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various non-limiting embodiments are further described with reference tothe accompanying drawings, in which

FIG. 1A illustrates a cross-section view of a MEMS structure inaccordance with a first embodiment;

FIG. 1B illustrates a cross-section view of a MEMS structure inaccordance with a second embodiment;

FIG. 2 illustrates a cross-section view of a MEMS structure inaccordance with a third embodiment;

FIG. 3 illustrates a cross-section view of a MEMS structure inaccordance with a fourth embodiment;

FIG. 4 illustrates a cross-section view of a MEMS structure inaccordance with a fifth embodiment;

FIG. 5 is a flowchart of a process for adding a piezoelectric layer to aMEMS structure;

FIG. 6 illustrates a cross-section view of a MEMS structure inaccordance with a sixth embodiment;

FIG. 7 illustrates a cross-section view of a MEMS structure inaccordance with a seventh embodiment;

FIG. 8 illustrates a cross-section view of a MEMS structure inaccordance with an eighth embodiment;

FIGS. 9A-9K illustrate cross-section views of a MEMS structure inaccordance with a ninth embodiment;

FIG. 10 illustrates a cross-section view of a MEMS structure inaccordance with a tenth embodiment;

FIG. 11 illustrates a cross-section view of a MEMS structure inaccordance with a eleventh embodiment;

FIGS. 12(a)(i), 12(a)(ii), 12(b)(i), and 12(b)(ii) illustratecross-section views of a MEMS structure in accordance with a twelfthembodiment;

FIGS. 13A-13H illustrate cross-section views of a MEMS structure inaccordance with a thirteenth embodiment;

FIGS. 14A-14C illustrate cross-section views of a MEMS structure inaccordance with a fourteenth embodiment;

FIG. 15 illustrates a block diagram of a piezoelectric acousticresonator based sensor, in accordance with various embodiments;

FIG. 16 illustrates a block diagram of a cross section of amicroelectromechanical systems (MEMS) piezoelectric acoustic resonator,in accordance with various embodiments;

FIG. 17 illustrates a frequency response of a MEMS piezoelectricacoustic resonator, in accordance with various embodiments;

FIG. 18 illustrates a block diagram of a cross section a MEMSpiezoelectric acoustic resonator including a material, in accordancewith various embodiments;

FIG. 19 illustrates a block diagram of a cross section of a portion ofan array of MEMS piezoelectric acoustic resonators being contacted by afinger, in accordance with various embodiments;

FIG. 20 illustrates a block diagram of a cross section of another MEMSpiezoelectric acoustic resonator, in accordance with variousembodiments;

FIG. 21 illustrates a frequency response of another MEMS piezoelectricacoustic resonator, in accordance with various embodiments;

FIG. 22 illustrates a block diagram of a cross section of a portion ofanother array of MEMS piezoelectric acoustic resonators being contactedby a finger, in accordance with various embodiments;

FIG. 23 illustrates a block diagram of a top view of electrodes of apiezoelectric acoustic resonator, in accordance with variousembodiments;

FIG. 24 illustrates a block diagram of a top view of other electrodes ofa piezoelectric acoustic resonator, in accordance with variousembodiments;

FIG. 25 illustrates a block diagram of a method for assembling a MEMSpiezoelectric acoustic resonator, in accordance with variousembodiments;

FIG. 26 illustrates a block diagram of a method for assembling anotherMEMS piezoelectric acoustic resonator, in accordance with variousembodiments;

FIG. 27 depicts a cross-section of an exemplary PMUT for fingerprintsensing, in accordance with various embodiments;

FIG. 28 depicts a cross-section of exemplary PMUT for fingerprintsensing on IC comprising exemplary PMUT bonded to an exemplarycomplementary metal oxide semiconductor (CMOS) wafer, in accordance withfurther non-limiting embodiments;

FIG. 29 depicts cross-sections of exemplary PMUT arrays having high fillfactor, in accordance with further non-limiting embodiments;

FIG. 30 depicts a cross-section of exemplary PMUT for fingerprintsensing on IC comprising exemplary PMUT integrated on an exemplary CMOSwafer, in accordance with further non-limiting embodiments;

FIG. 31 depicts a cross-section of an exemplary CMOS wafer suitable forincorporation of aspects of the subject disclosure directed tofabrication of exemplary PMUT and PMUT arrays for fingerprint sensing onIC comprising exemplary one or more exemplary PMUTs integrated onexemplary CMOS wafer, in accordance with further non-limitingembodiments;

FIG. 32 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary cavities, in accordance with further aspectsdescribed herein directed to a non-limiting cavity deposition etchprocess;

FIG. 33 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary sacrificial materials, in accordance with furtheraspects described herein directed to non-limiting amorphous silicondeposition and subsequent chemical-mechanical planarizing processes;

FIG. 34 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary silicon dioxide (SiO₂) layers, in accordance withfurther aspects described herein directed to a non-limiting silicondioxide deposition process;

FIG. 35 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary seal holes, in accordance with further aspectsdescribed herein directed to a non-limiting release hole openingprocess;

FIG. 36 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary cavities, in accordance with further aspectsdescribed herein directed to a non-limiting release etch process;

FIG. 37 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary seal hole seals, in accordance with furtheraspects described herein directed to non-limiting seal deposition andetch back processes;

FIG. 38 depicts a cross-section of an exemplary CMOS wafer comprisingexemplary aluminum nitride (AlN) seed layer, molybdenum (Mo) layer, andAlN stacking layer, in accordance with further aspects described hereindirected to non-limiting AlN Seed/Mo/AlN deposition processes;

FIG. 39 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary SiO₂ layers, in accordance with further aspectsdescribed herein directed to a non-limiting hard mask depositionprocess;

FIG. 40 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary bottom contacts, in accordance with furtheraspects described herein directed to a non-limiting bottom contact tomolybdenum fabrication process;

FIG. 41 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary vias, in accordance with further aspects describedherein directed to a non-limiting wafer via etch process;

FIG. 42 depicts a cross-section of an exemplary CMOS wafer comprising anexposed MN surface, in accordance with further aspects described hereindirected to a non-limiting hard mask removal process;

FIG. 43 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary SiO2 spacers, in accordance with further aspectsdescribed herein directed to a non-limiting SiO2 spacer fabricationprocess;

FIG. 44 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary top electrodes, in accordance with further aspectsdescribed herein directed to a non-limiting top electrode fabricationprocess;

FIG. 45 depicts exemplary PMUT for fingerprint sensing on IC comprisingexemplary PMUT integrated on exemplary CMOS wafer as described aboveregarding FIG. 30, and which exemplary CMOS wafer comprises one or moreexemplary passivation layers, in accordance with further aspectsdescribed herein directed to a non-limiting passivation process;

FIG. 46 depicts an exemplary flowchart of non-limiting methodsassociated with a various non-limiting embodiments of the subjectdisclosure; and

FIG. 47 depicts another exemplary flowchart of non-limiting methodsassociated with a various non-limiting embodiments of the subjectdisclosure.

DETAILED DESCRIPTION

While a brief overview is provided, certain aspects of the subjectdisclosure are described or depicted herein for the purposes ofillustration and not limitation. Thus, variations of the disclosedembodiments as suggested by the disclosed apparatuses, systems, andmethodologies are intended to be encompassed within the scope of thesubject matter disclosed herein.

One or more embodiments are now described with reference to thedrawings, wherein like reference numerals are used to refer to likeelements throughout. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the various embodiments. It may be evident,however, that the various embodiments can be practiced without thesespecific details, e.g., variations in configurations, processes, and/ormaterials. In other instances, well-known structures and devices areshown in block diagram form in order to facilitate describing theembodiments in additional detail.

In the described embodiments microelectromechanical systems (MEMS)refers to a class of structures or devices fabricated usingsemiconductor-like processes and exhibiting mechanical characteristicssuch as the ability to move or deform. MEMS often, but not alwaysinteract with electrical signals. MEMS devices include but are notlimited to gyroscopes, accelerometers, magnetometers, pressure sensors,and radio-frequency components. Silicon wafers containing MEMSstructures are referred to as MEMS wafers.

In the described embodiments, MEMS device may refer to a semiconductordevice implemented as a microelectromechanical system. MEMS structuremay refer to any feature that may be part of a larger MEMS device. Anengineered silicon-on-insulator (ESOI) wafer may refer to a SOI waferwith cavities beneath the silicon device layer or substrate. Handlewafer typically refers to a thicker substrate used as a carrier for thethinner silicon device substrate in a silicon-on-insulator wafer. Handlesubstrate and handle wafer can be interchanged.

In the described embodiments, a cavity may refer to an opening orrecession in a substrate wafer and enclosure may refer to a fullyenclosed space. Bond chamber may be an enclosure in a piece of bondingequipment where the wafer bonding process takes place. The atmosphere inthe bond chamber determines the atmosphere sealed in the bonded wafers.

Additionally, a system and method in accordance with the presentinvention describes a class of RF MEMS devices, sensors, and actuatorsincluding but not limited to switches, resonators and tunable capacitorsthat are hermetically sealed and bonded to integrated circuits that mayuse capacitive sensing and electrostatic, magnetic, or piezoelectricactuation.

FIG. 1A illustrates a cross-section view of a MEMS structure 100 inaccordance with a first embodiment. FIG. 1A shows a MEMS structure withaddition of metal on the silicon structural layer. The structureincludes a CMOS wafer 102 bonded to a MEMS wafer 104. The MEMS wafer 104comprises a silicon device layer 106 fusion bonded to a handle wafer 108through an oxide layer 109. A MEMS aluminum 110 metal layer is added tothe silicon device layer 106. Adding a metal layer lowers theresistivity of the MEMS structure over that of just the silicon devicelayer 106 making it more attractive for applications requiring lowparasitics (ex. RF MEMS, Lorentz force sensors, etc.). In thisembodiment, the connection between CMOS wafer 102 and MEMS wafer 104 iscreated through the silicon stand-offs 112 using an aluminum-germaniumeutectic bond formed by germanium 111 and aluminum 113. Apart from thestand-offs 112 the bulk of the current is carried by the metal layers117. In an embodiment, spacers 114 composed of an insulating materialsuch as Silicon Oxide or Silicon Nitride may be placed on bottom metallayer 117 to reduce stiction and control the gap between the top metallayer 110 and the bottom metal layer 117.

FIG. 1B illustrates a cross-section view of a MEMS structure 100′ inaccordance with a second embodiment. FIG. 1B shows a MEMS structure withadditional insulating layer 112 a deposited onto the MEMS aluminum 110and insulating layer 112 b deposited onto the bottom electrode 117 toprevent shorting and create a well-defined capacitive gap when themovable MEMS structure consisting of the silicon device layer 106, MEMSaluminum 110, and insulating layer 112 a are brought into contact withthe electrodes on the CMOS wafer 102.

FIG. 2 illustrates a cross-section view of a MEMS structure 200 inaccordance with a third embodiment. FIG. 2 shows a MEMS structuresimilar to FIG. 1A. However, in this embodiment the electricalconnection between the CMOS wafer 102′ and the MEMS wafer 104′ occursthrough physical contact between the CMOS aluminum 204 on the CMOS wafer102′ and the MEMS aluminum 110′ on the MEMS wafer 104′ connected by anAluminum-Germanium layer created by the eutectic reaction betweengermanium 206 and CMOS aluminum 113′ on the CMOS wafer 102′ and the MEMSaluminum 110′ on the MEMS wafer 104′. One possible risk of thisembodiment is a preferential reaction of the germanium 206 with the MEMSaluminum 110′ (since that is the layer it is directly deposited on) witha possibly insufficient reaction with the CMOS aluminum 113′. Theinsufficient reaction may lead to poor bonds and marginal electricalconnections.

FIG. 3 illustrates a cross-section view of a MEMS structure 300 inaccordance with a fourth embodiment. FIG. 3 shows a MEMS structureidentical to FIG. 2 with the exception of a barrier layer 302 depositedbetween the MEMS aluminum 110″ and germanium 206′. The barrier layer 302is electrically conductive and makes an electrical contact with aluminumupon physical contact. The objective of the barrier layer 302 is toprevent a eutectic reaction between the MEMS aluminum 110″ and germanium206′, leaving germanium 206′ to eutectically react with the CMOSaluminum 113″. One such barrier layer may be Titanium Nitride. Duringthe eutectic reaction, the CMOS aluminum 113″ will mix with germanium206′ creating an electrical contact and physical bond to the barrierlayer 302 on the MEMS aluminum 110″, thereby creating an electricalcontact between the CMOS wafer 102″ and MEMS wafer 104″.

FIG. 4 illustrates a cross-section view of a MEMS structure 400 inaccordance with a fifth embodiment. FIG. 4 shows a MEMS structureidentical to FIG. 3, but with an insulating layer 402 deposited betweenthe MEMS aluminum 110′″ and silicon device layer 106′″ therebyelectrically insulating the silicon from the metal. The insulating layer402 is needed in cases where it is not desirable to carry any electricalsignal in the silicon layer (for example in RF applications where signaltransmission in the silicon would produce a power loss). In thisembodiment, at RF frequencies the MEMS aluminum 110′″ is stillcapacitively coupled to the silicon device layer 106′″ through theinsulating layer 402. To achieve sufficient isolation the insulatinglayer must be sufficiently thick to minimize capacitance or the siliconmust be sufficiently resistive so as to minimize electrical signalcoupling into it.

FIG. 5 is a flowchart of a process for adding metal and piezoelectriclayers to a MEMS structure. The process starts with an Engineered SOI502. A first metal layer (metal 1) is deposited onto the device siliconsurface via step 504 followed by the piezoelectric layer deposition(e.g., Aluminum Nitride or PZT) pattern and etch via step 506. Next asecond metal layer (Metal 2) deposited onto the wafer to serve as a topelectrode for the piezoelectric layer as well as to provide electricalcontact between Metal 1 and the CMOS substrate via step 508. A germaniumlayer is deposited onto Metal 1 and patterned to define germanium padsin regions where bonding to CMOS will take place via step 510. Next, theMEMS wafer is bonded to a CMOS wafer such that germanium padseutectically react with aluminum pads on the CMOS creating electricaland physical contact between the CMOS aluminum and MEMS Metal 2 via step512.

FIG. 6 illustrates a cross-section view of a MEMS structure 600 inaccordance with a sixth embodiment that utilizes a piezoelectric layer.Adding a piezoelectric layer 602 enables a range of applicationsincluding acoustic resonators and filters and piezo-actuated devices. Tooperate, the piezoelectric layer 602 typically requires a bottomelectrode 604 and top electrodes 606. The bottom electrode 604 maycomprise a first metal layer (metal 1) (Ex. Aluminium, Ruhtenium,Tungsten, Molybdenum or Platinum). In another embodiment, a silicondevice layer can be used as a bottom electrode 604. The top electrode606 and interconnect 610 are composed of a second metal layer (metal 2)(Ex. Aluminum). The top electrode 606 and interconnect 610 make physicaland electrical contact to the CMOS aluminum pads 608 using an AluminumGermanium bond. The bottom electrode 604 may make physical andelectrical contact to the interconnect 610 thereby connecting to theCMOS wafer. Electrical potentials may be applied between top electrodes606 and the bottom electrode 604 or between individual top electrodes606. These potentials create electric fields to induce strains withinthe piezoelectric material.

FIG. 7 illustrates a cross-section view of a MEMS structure 700 inaccordance with a seventh embodiment. FIG. 7 shows the same structure asin FIG. 6 with an addition of a silicon dioxide layer 702 between thedevice layer silicon 106 and metal layer, 604″. The silicon dioxidelayer, 702 serves as a temperature stabilization layer that improvesfrequency stability of the resonator or filter over temperature byoffsetting the positive Young's modulus temperature coefficient ofsilicon with the negative Young's modulus temperature coefficient ofsilicon oxide.

FIG. 8 illustrates a cross-section view of a MEMS structure 800 inaccordance with a eighth embodiment. FIG. 8 shows the same structure asin FIG. 7 with an addition of a patterned bottom electrode 604″. Bypatterning the bottom electrode 604″, multiple potentials may be appliedto different sections of the bottom surface of the piezoelectricmaterial 602, leading to more design flexibility and potentially moreefficient devices. For resonator applications, for example, the abilityto input electrical signals on both the bottom and top of thepiezoelectric structure can lead to higher coupling efficiency. Infurther embodiments, the subject application provides disclosure of amicroelectromechanical system (MEMS) integration flow to incorporatealuminum nitride (AlN) on an engineering substrate and a top electrodelayer combined with aluminum germanium (AlGe) with complementarymetal-oxide-semiconductor (CMOS) wafers/layers/substrates.

In addition to the foregoing, the subject application further describesa MEMS integration flow that comprises starting wafers/layers/substrates(e.g., complementary metal-oxide-semiconductor (CMOS)wafers/layers/substrates, MEMS handle wafers/layers/substrates, and/orMEMS device wafers/layers/substrates) and a plurality of masking layers,for example, ten masking layers, though, as will be appreciated by thoseof ordinary skill, a fewer or a greater number of masking layers can beutilized without unduly departing from the generality and scope of thesubject disclosure.

Typically, the MEMS handle wafers/layers/substrates can be patternedwith back-side alignment mark layers used for front-to-back alignmentafter fusion bonding. Cavities that define suspended MEMS structures canalso be etched in a front-side of the MEMS handlewafers/layers/substrates. The MEMS handle layers/wafers/substrates canthen be oxidized and fusion-bonded to MEMS devicelayers/wafers/substrates.

The MEMS device layers/wafers/substrates can, for example, comprisesilicon (Si) structural layers that can be ground and polished to targetthicknesses, at which point aluminum nitride seed layers can be disposedover a surface of the silicon structural layers, molybdenum layers canbe deposited over the aluminum nitride seed layers, aluminum nitridestacking layers can be deposited over the molybdenum layers, and/orsilicon dioxide standoff layers can be disposed on the aluminum nitridestacking layers.

The silicon dioxide standoff layers can be etched on the MEMS devicelayers/wafers/substrates to provide separations between the MEMSstructures and the complementary metal-oxide-semiconductorwafers/layers/substrates. The aluminum nitride (AlN) stacking layers canthen be patterned through a silicon dioxide hard mask with structures,bottom contacts, and/or aluminum nitride top contact masks.Additionally, aluminum, titanium, and germanium can then be deposited insequence from bottom to top and patterned with germanium pads andelectrodes. The silicon device layer can then be patterned and etchedusing, for instance an anisotropic etch process used to create deeppenetration, steep-sided holes and trenches in layers/wafers/substrates,typically with high aspect ratios, such as deep reactive-ion etching(DRIE), to define release structures. Generally, the combination of thestructures and release layers that define the fully released structureare formed on the upper cavity.

A bottom cavity can be etched in the complementarymetal-oxide-semiconductor layer/wafer to allow clearance forout-of-plane moving of the MEMS structures (e.g., combinations ofsilicon and aluminum nitride stacking layers) or damping control. TheMEMS and complementary metal-oxide-semiconductorwafers/layers/substrates can then be bonded using aluminum-germanium(Al—Ge) eutectic bonding to create hermetic seals around the MEMSstructures as well as electrical interconnects between the MEMSstructures and complementary metal-oxide-semiconductor circuits.Thereafter, the bonded wafer/layer can be thinned on the MEMS side to adesired thickness and a port can be formed on the polished side of theMEMS wafer/layer to create access to the surrounding environment.Silicon tabs on the MEMS wafer/layer can thereafter be removed using,for example, a dicing process to expose the complementarymetal-oxide-semiconductor wire-bond pads.

In accordance with the foregoing and with reference to FIG. 9A, across-section of a MEMS device 900 is illustrated. The MEMS 900 cancomprise a handle wafer/layer/substrate 904 that can have been patternedwith back-side alignment mark layers to be employed for front-to-backalignment after fusion bonding. Further, a front side of handlewafer/layer/substrate 904 can have been etched to form cavities 902. Asdepicted handle wafer/layer/substrate 904 can be formed of a siliconlayer/substrate into which cavities 902 can have been etched. To thehandle wafer/layer/substrate 904 inclusive of cavities 902 a silicondioxide layer/substrate 906 can be deposited on the siliconlayer/substrate 904 thereby overlaying silicon layer/substrate 904 andcavities 902 formed therein. Disposed and/or deposited over silicondioxide layer/substrate 906 and fusion bonded to the silicon dioxidelayer/substrate 906 can be a substrate/layer formed of silicon 908. Inaccordance with an embodiment, the handle wafer/layer/substrate 904inclusive of formed cavities 902 and silicon dioxide layer 906 can bereferred to as an engineered substrate, and for purposes of thisdisclosure can be referred to a the MEMS handle layer.

With reference to FIG. 9B that depicts a further cross-sectional view ofMEMS device 900, in addition to the above noted silicon layer/substrate904 inclusive of etched cavities 902, silicon dioxide layer/substrate906 (silicon layer/substrate 904 inclusive of etched cavities 902 andsilicon dioxide layer/substrate 906 can form and be referred to as theMEMS handle layer/wafer/substrate), and a substrate/layer 908 formed ofsilicon, silicon dioxide standoffs 916 can be formed on the MEMS handlelayer/wafer/substrate by, for example, successively depositing aluminumnitride seed layers 910, molybdenum layers 912, and aluminum nitridestacking layers 914 over silicon substrate/layer 908, prior to etchingand/or forming silicon dioxide standoffs 916. The additional depositedor disposed layers comprising the aluminum nitride seed layers 910,molybdenum layers 912, aluminum nitride stacking layers 914, and silicondioxide standoffs 916 over silicon substrate/layer 908 can be referredto the MEMS device layer/wafer/substrate and/or piezoelectriclayer/wafer/substrate.

Silicon substrate layer 908 can be the silicon structural layer of theMEMS device layer to which the MEMS handle layer (e.g., siliconlayer/substrate 904 inclusive of etched cavities 902 and silicon dioxidelayer/substrate 906) can have been fusion bonded to the MEMS devicelayer/wafer/substrate (e.g., silicon structural substrate/layer 908,aluminum nitride seed layers 910, molybdenum layers 912, aluminumnitride stacking layers 914, and standoffs 916). It should be noted thatthe MEMS handle layer, prior to fusion bonding of the MEMS handle layerto the MEMS device layer, can typically have been oxidized and thesilicon structural layer/substrate 908 of the MEMS device layer can havebeen ground and polished to a target or defined thickness prior todeposition of the aluminum nitride seed layers 910, molybdenum layers912, aluminum nitride stacking layers 914, and standoffs 916 formed ofsilicon dioxide. Standoffs 916 are typically formed on the MEMS devicelayer to provide separation between the MEMS structure and a CMOSwafer/layer/substrate.

FIGS. 9C-9E provide illustration of a further cross-sectional view ofMEMS device 900 including the layers described above in connection withFIGS. 9A-9B. In FIG. 9C, structure can be defined and separate bottomelectrodes 920 can be carved out by first disposing or depositing asilicon dioxide hard mask 918 over the aluminum nitride stacking layers914 and standoffs 916 and thereafter etching through silicon dioxidehard mask 918 to define the structure and carve out separate bottomelectrodes 920. As will be observed, the etching process etches throughlayers/substrates respectively formed of silicon dioxide hard mask 918,aluminum nitride 914, molybdenum 912, and aluminum nitride seed layer910, to the silicon structural layer/substrate 908. In FIG. 9D, a bottomelectrodes contact 922 can be created. In FIG. 9E a opening etch onsilicon dioxide layer 918 can be performed to define aluminum nitridetop contacts 924 and avoids unnecessary HBAR resonance from the pad.Defining the structure and carving out the bottom electrodes 920,creating bottom electrode contacts 922, and defining aluminum nitridetop contacts 924, as depicted in FIGS. 9C-9E, can be undertaken bypatterning the aluminum nitride stacking layers through silicon dioxidehard mark 918.

As illustrated in FIG. 9F aluminum and titanium layers 926 are depositedfor the purposes of top electrode material deposition and then germaniumlayers 928 are deposited over the aluminum and titanium layers 926 sothat germanium pads 928 and electrodes 930 can be patterned as depictedin FIGS. 9G-H. The device layer can be overlaid with a layer ofphoto-resist 932 and patterned and etched using deep reactive-ionetching (DRIE) to define release structures, as depicted in FIG. 91.Only the combination of the structure and release layer can define thefully released structure 934 (See FIG. 9J) in the cavity 902.

As depicted in FIG. 9J, a cavity 938 is etched into a CMOS wafer 936 toallow clearance for out-of-plane moving MEMS structures 934 and/ordamping control, and thereafter the CMOS wafer 936 and MEMS device wafer940 are bonded using an Aluminum-Germanium eutectic bond to create ahermetic seal around MEMS structure 934 and CMOS circuits and form abonded wafer 942. The eutectically bonded wafer 942 can then be thinned,for instance, on the MEMS wafer side, to a defined or desired thicknessand a port 944 can be formed on a polished side of the MEMS wafer 942 tocreate access to the surrounding environment, as illustrated in FIG. 9K.Additionally, silicon tabs on the MEMS wafer 942 can be removed using adicing process to expose CMOS wire bond pads.

In accordance with the foregoing and in an additional embodiment asillustrated in FIG. 10, subsequent to defining structure and carving outseparate bottom electrodes 920, as illustrated in FIG. 9C, but prior tocreating bottom electrode contacts 922, as depicted in FIG. 9D, apartial silicon etch can be performed wherein structural silicon layer908 (e.g., the structural silicon layer of the MEMS device wafer) canpartially be further etched 1002. The partial etch 1002 can be performedto partially thin down the silicon device layer (e.g., structuralsilicon layer 908). The partial etch 1002 can be accomplished with astructure layer mask through silicon etch or silicon deep reactive-ionetching. It should be noted that the partial etch 1002 can be anadditional etch to that previously performed to define structure andcarve out separate bottom electrodes 920 as elucidated above inconnection with FIG. 9C. Additionally and/or alternatively, partial etch1002 and the etch performed to define structure and carve out separatebottom electrodes 920, as depicted in FIG. 9C, can be accomplished in asingle act without unduly and/or unnecessarily departing from the intentand generality of the subject disclosure.

In a further additional aspect or embodiment, as illustrated in FIG. 11,an additional act of can be performed subsequent to etching port 944 ona polished side of the MEMS wafer 942 (see e.g., FIG. 9K). In accordancewith this aspect, an infra-red (IR) absorption layer 1102 can bedeposited on the back of the MEMS handle wafer 940. The infra-red (IR)absorption layer 1102, as illustrated, can be disposed not only on theback of the MEMS handle wafer 940 but also in the previously etched port944.

In accordance with a further disclosed aspect or embodiment, asillustrated in FIG. 12 additional and/or alternative standoff 916formations techniques can be employed. As illustrated in FIG. 12(a)(i) alayer of silicon 908 can be deposited over the MEMS handlelayer/wafer/substrate (e.g., silicon layer/wafer/substrate 904 inclusiveof cavities 902 and silicon dioxide layer/substrate 906) and thereafterthe deposited layer of silicon 908 can be partially etched to formstandoffs 916, thus, referring back to FIG. 9A and as illustrated inFIG. 12(a)(i), standoffs 916 can have been formed from the structuralsilicon layer 908 of the MEMS device layer or piezoelectriclayer/wafer/substrate. Alternatively, as depicted in FIG. 12(a)(ii)rather than partially etching into structural silicon layer 908,structural silicon layer 908 can be overlaid with a silicon dioxidelayer and thereafter the deposited silicon dioxide layer can bepatterned to create or form standoffs 916, as illustrated in FIG.12(a)(ii).

Thereafter, and still with reference to FIG. 12, deposition ofpiezoelectric stacking layers 1202, as described and illustrated inconnection with FIGS. 9C-9K, can be carried out as respectively depictedin FIGS. 12(b)(i) and 12(b)(ii). In the context of FIG. 12(b)(i) it willbe observed that the subsequent piezoelectric stacking layers 1202, asdescribed in relation to FIGS. 9C-9K, overlay silicon standoffs 916,whereas, in connection with FIG. 12(b)(ii), the successive layers thatcomprise the piezoelectric stacking layers 1202, as disclosed withrespect to FIGS. 9C-9K, are deposited over silicon dioxide standoffs916.

FIG. 13 illustrates an additional and/or alternative process flow thanthat described and disclosed in connection with FIGS. 9A-9K. In thisinstance, and as depicted in FIG. 13A, and as has been described abovein relation to FIG. 12(a)(i), silicon standoffs 916 can have been formedby patterning and/or partially etching structural silicon layer 908.Thereafter, the piezoelectric layer stacking (e.g., aluminum nitrideseed layers 910, molybdenum layer 912, and aluminum nitride stackinglayer 914) described earlier with respect to FIG. 9B can be reduced toonly an aluminum nitride layer 1302, wherein an aluminum nitride layer1302 is overlaid and patterned 1304 on top of the structural siliconlayer 908 inclusive of the formed silicon standoffs 916. As illustratedin FIGS. 13B-13H, the structural silicon layer 908 inclusive of thesilicon standoffs 916 can be used as bottom electrodes. In FIG. 13C thealuminum nitride layer 1302 can be overlaid with aluminum and titaniumlayers 1306. As will be noted in relation to FIG. 13C, patterning inaluminum nitride layer 1302 at 1304 will be filled by the aluminum andtitanium layers 1306.

In FIG. 13D germanium pads 1308 can be defined, wherein a germaniumlayer can be overlaid aluminum and titanium layers 1306 to form thegermanium pads 1308. Further, in FIG. 13E the previously depositedaluminum and titanium layers 1306 can be selectively patterned to definealuminum and titanium pads 1310 and to expose the underlying aluminumnitride layer 1302. In FIG. 13F a silicon dioxide hard mask 1312 can bedeposited over defined germanium pads 1308, aluminum and titanium pads1310, and exposed aluminum nitride layer 1302 and an etch or patterningperformed to define the structure 1314.

Once structure 1314 has been defined, a CMOS wafer 936 can beeutectically bonded to the MEMS device wafer 1316, in a manner similarto that described in the context of FIG. 9J and illustrated in FIG. 13G.Further, on completion of the eutectic bonding of the CMOS wafer 936 tothe MEMS device wafer 1316, a port 1318 can be formed on a polished sideor surface of the MEMS device wafer 1316, as illustrated in FIG. 13H.

With reference now to FIGS. 14A-14C, and initially in reference to FIG.14A, in order to provide protection to sidewalls 1402 during the variousetching and/or patterning phases that can be employed to construct thedescribed micro-electrical-mechanical device, in accordance with anembodiment, and as illustrated in FIG. 14B a silicon dioxide layer 1404can be deposited to overlay the layers previously described in thecontext of FIG. 9E. It will be observed on examination of FIG. 14B thatthe silicon dioxide layer 1404 has been disposed to cover the sidewalls1402 as well as bottom electrodes 920 and the bottom electrodes contact922. Additionally, as will also have been observed on inspection of FIG.14B, the deposited silicon dioxide layer 1404 will also have covered thealuminum nitride top contact 924. The deposition and patterning ofsilicon dioxide layer 1404 provides isolation Once the silicon dioxidelayer 1404 has been deposited as illustrated in FIG. 14B, the silicondioxide layer 1404 can undergo a blank reactive-ion etch to createsidewall protection 1406.

In accordance with the foregoing, the subject application discloses inone or more various embodiments and aspects a MEMS device, comprising: afirst silicon substrate comprising: a handle layer comprising a firstsurface and a second surface, the second surface comprises a cavity; aninsulating layer deposited over the second surface of the handle layer;a device layer having a third surface bonded to the insulating layer anda fourth surface; a piezoelectric layer deposited over the fourthsurface of the device layer; a metal conductivity layer disposed overthe piezoelectric layer; a bond layer disposed over a portion of themetal conductivity layer; and a stand-off formed on the first siliconsubstrate; wherein the first silicon substrate is bonded to a secondsilicon substrate, comprising: a metal electrode configured to form anelectrical connection between the metal conductivity layer formed on thefirst silicon substrate and the second silicon substrate.

In accordance with the foregoing, the stand-off can be formed on thepiezoelectric layer and can be formed as a silicon layer or as a silicondioxide layer deposited on the device layer. Additionally and/oralternatively, the stand-off can be formed of silicon dioxide depositedon the piezoelectric layer.

Further, the piezoelectric layer can be patterned and etched to form asidewall in the piezoelectric layer, wherein a first dielectric layercan be interposed between the piezoelectric layer and the metalconductive layer, and a second dielectric layer can be disposed on thesidewall of the piezoelectric layer. In addition, an opening in thehandle layer can be exploited to expose the device layer, an orifice inthe device layer can be used to expose the piezoelectric layer, and thedevice layer can include an aperture.

In accordance with a disclosed aspect the device layer can beselectively or partially removed, the piezoelectric layer can in anembodiment comprise aluminum nitride or in another embodiment cancomprise: an aluminum nitride (AlN) seed layer, a bottom metal layer,and an aluminum nitride (AlN) layer. Further, an infra-red (IR)absorption layer can be deposited on a portion of the device layerand/or the infra-red (IR) absorption layer can be deposited on a portionof the piezoelectric layer.

In accordance with a further embodiment, a method is described anddisclosed. The method can comprise a sequence of machine executableoperations that can include depositing an insulation layer over a handlelayer that comprises a first surface and a second surface, wherein thesecond surface comprises a cavity and the insulation layer is formed onthe second surface of the handle layer; bonding a first surface of adevice layer to the insulation layer; depositing a piezoelectric layeron a second surface of the device layer; depositing a metal conductivitylayer over the piezoelectric layer; partially depositing a bond layerover the metal conductivity layer; forming a stand-off on the secondsurface of the device layer; and establishing an electrical connectionbetween the metal conductivity layer and a silicon substrate.

Further machine executable method operations can include: depositing asilicon layer or a silicon dioxide layer to form the stand-off;depositing a silicon dioxide layer to form a stand-off positioned on thepiezoelectric layer; patterning and etching of the piezoelectric layerto form a sidewall; interposing a first dielectric layer between thepiezoelectric layer and the metal conductive layer; disposing a seconddielectric layer on the sidewall of the piezoelectric layer; exposingthe device layer via a first opening in the handle layer; and exposingthe piezoelectric layer through the first opening and a second openingin the device layer.

Additional machine executed method acts can also include: selectivelyremoving a portion of the device layer; depositing an infra-red (IR)absorption layer on a selected portion of the device layer; anddepositing an infra-red (IR) absorption layer on a selected portion ofthe piezoelectric layer.

In accordance with further embodiments the disclosure describes amicroelectromechanical device that can comprise: a first siliconsubstrate bonded to a second silicon substrate, comprising: an electrodeon the second silicon substrate that electrically contacts aconductivity layer disposed on the first silicon substrate; theconductivity layer on the first silicon substrate is disposed over apiezoelectric layer on the first silicon substrate; the piezoelectriclayer on the first silicon substrate is deposited over a device layerthat comprises a stand-off formed on the first silicon substrate; andthe device layer on the first silicon substrate is bonded to andielectric layer that is deposited over a surface of a handle layer onthe first silicon substrate that comprises a cavity.

In addition to the foregoing, the subject application further describesMEMS devices and fingerprint sensing. There are two kinds of fingerprint sensors, namely swipe-based and area-based. For mobileapplications, optical method is too bulky and expensive; thermal andswipe-based RF method are not the favored due to user experience;area-based ultrasound and RF sensors have challenges to lower themanufacturing cost. In general, above conventional fingerprint sensortechnologies are subject to errors due to finger contamination, sensorcontamination, imaging errors, etc. Various embodiments disclosed hereinprovide for improved fingerprint sensor performance by measuring afrequency response of a piezoelectric acoustic resonator.

For example, a device can include an array of piezoelectric transducers,and an array of cavities that has been attached to the array ofpiezoelectric transducers to form an array of resonators, e.g., an arrayof MEMS piezoelectric acoustic resonators. A resonator, e.g., a membraneresonator, a Helmholtz resonator, etc. of the array of resonators can beassociated with a first frequency response, e.g., a resonant frequencyof the resonator, a Q factor of the resonator, etc. corresponding to adetermination that the resonator has a non-touch baseline condition.Then a second frequency response, e.g., increase in resonant frequencyof the resonator, decrease in Q factor of the resonator, etc.corresponding to a determination that the resonator has been touched,e.g., by the finger ridge. Thus the finger print map can be determinedaccording to the frequency response changes of resonators in theresonator array.

In an embodiment, the array of piezoelectric transducers can include apiezoelectric material; a first set of electrodes that has been formed afirst side of the piezoelectric material; and a second set of electrodesthat has been formed on second side of the piezoelectric material—apiezoelectric transducer of the array of piezoelectric transducerscorresponding to the resonator including a first electrode of the firstset of electrodes and a second electrode of the second set ofelectrodes.

In another embodiment, the piezoelectric transducer comprises a portionof the resonator, e.g., a membrane resonator, that has been touched. Inyet another embodiment, a first end of a cavity of array of cavitiescorresponding to a portion of the resonator, e.g., a Helmholtzresonator, that has been touched is smaller than a second end of thecavity. In an embodiment, the first end of the cavity is open to theenvironment, e.g., air adjacent to the device, etc. In anotherembodiment, the cavity has been filled with a first materialcorresponding to a first acoustic velocity that is different from asecond acoustic velocity corresponding to a second material that isadjacent to, surrounding, etc. the cavity.

Another embodiment can include a system, e.g., a piezoelectric acousticresonator based fingerprint sensor, etc. that can include an array ofpiezoelectric transducers; an array of cavities that has been attachedto the array of piezoelectric transducers to form an array ofresonators; a memory to store instructions; and a processor coupled tothe memory, that facilitates execution of the instructions to performoperations, comprising: determining a frequency response of a resonatorof the array of resonators—the resonator including a piezoelectrictransducer of the array of piezoelectric transducers and a cavity of thearray of cavities; and determining that the resonator has been touched,e.g., by a finger, etc. in response determining that a change in thefrequency response satisfies a defined condition, e.g., a resonantfrequency of the resonator has increased, a Q factor of the resonatorhas decreased, etc.

In one embodiment, a first portion of the cavity, e.g., corresponding toa portion of the resonator that has been touched, is smaller than asecond portion of the cavity. In another embodiment, the first portionof the cavity is open to the environment. In yet another embodiment, thecavity has been filled with a first material corresponding to a firstacoustic velocity that is different from a second acoustic velocitycorresponding to a second material that is adjacent to the cavity.

One embodiment can include a method including forming an array ofpiezoelectric transducers on a first substrate; forming one or moreportions of an array of cavities using a second substrate; and attachingthe array of piezoelectric transducers to the second substrate to forman array of resonators. A resonator, e.g., a membrane resonator, aHelmholtz resonator, etc. of the array of resonators can be associatedwith a first frequency response with respect to, e.g., a resonantfrequency of the resonator, a Q factor of the resonator, etc.corresponding to a determined non-touch of the resonator. Further, theresonator can be associated with a second frequency response withrespect to, e.g., the resonant frequency, the Q factor, etc.corresponding to a determined touch of the resonator. Furthermore, themethod can include removing the first substrate from the array ofpiezoelectric transducers.

In an embodiment, the forming of the array of piezoelectric transducerscan include forming a first set of electrodes on a first side of apiezoelectric material, and forming a second set of electrodes on asecond side of the piezoelectric material—a piezoelectric transducer ofthe array of piezoelectric transducers corresponding to the resonatorcan include a first electrode of the first set of electrodes and asecond electrode of the second set of electrodes.

In another embodiment, the method can include filling a cavity of thearray of cavities corresponding to the resonator, e.g., the Helmholtzresonator, with a material having a first acoustic velocity that isdifferent from a second acoustic velocity of the second substrate.

Referring now to FIG. 15, a block diagram of a piezoelectric acousticresonator based sensor 1500 is illustrated, in accordance with variousembodiments. Piezoelectric acoustic resonator based sensor 1500 includescontrol component 1502 and array of piezoelectric acoustic resonators1505. Control component 1502, e.g., a system, an application specificintegrated circuit (ASIC), etc. can include computing device(s), memorydevice(s), computing system(s), logic, etc. for generating stimuli,e.g., via TX component 1506, detecting a response to the stimuli, e.g.,via RX component 1508, and determining, e.g., via processing component1504 based on the stimuli and the response to the stimuli, a frequencyresponse, e.g., a change in a resonant frequency, a change in a Qfactor, etc. of a piezoelectric acoustic resonator (1510, 1605 (seebelow), 2005 (see below), etc.) of array of piezoelectric acousticresonators 1505. In this regard, processing component 1504 candetermine, based on the frequency response, whether the piezoelectricacoustic resonator has been touched, e.g., by a ridge of a finger, andfurther derive a fingerprint based on determining which piezoelectricacoustic resonator(s) 1510 of array of piezoelectric acoustic resonators1505 have been touched.

FIG. 16 illustrates a block diagram of a cross section of MEMSpiezoelectric acoustic resonator 1605, in accordance with variousembodiments. MEMS piezoelectric acoustic resonator 1605, e.g., aHelmholtz resonator, includes cavity 1640 that has been formed by,within, etc. substrate 1650, e.g., a silicon based material, etc. In theembodiment illustrated by FIG. 16, cavity 1640 includes an opening thatis exposed to the environment, e.g., air. Further, a cross section of afirst end, or top portion, of cavity 1640 is smaller than a crosssection of a second end, or bottom portion, of cavity 1640, e.g.,enabling cavity 1640 to experience a resonant frequency (f_(H)), orHelmholtz resonance, e.g., as defined by Equation (1) below:

$\begin{matrix}{{f_{H} = {\frac{v}{2\pi}\sqrt{\frac{A}{V_{0}L_{eq}}}}},} & (1)\end{matrix}$where A is the cross-sectional area of the top portion, or “neck”, ofcavity 1640, V₀ is the static volume of cavity 1640, L_(eq) is theequivalent length of the neck with end correction, and v is the speed ofsound in a gas as given by Equation (2) below:v=331.3+0.606·θwhere θ is the ambient temperature in degree Celsius.

MEMS piezoelectric acoustic resonator 1605 includes piezoelectrictransducer 1607, which includes top electrode 1610, piezoelectricmaterial 1620, e.g., piezoelectric membrane, polyvinylidene fluoride(PVDF), etc. and bottom electrode 1630. In one embodiment, top electrode1610 and bottom electrode 1630 can be manufactured from a conductivematerial, e.g., metal, and control component 1502 can generate and applya stimulus, e.g., a pulse signal, a frequency sweep, an alternatingcurrent (AC) voltage, an AC current, etc. to piezoelectric transducer1607 via top electrode 1610 and bottom electrode 1630. As illustrated byFIG. 17, control component 1502 can measure, e.g., utilizing a networkanalyzer, etc. based on the stimulus, e.g., based on a Fourier transformanalysis, resonant frequency 1710, e.g., corresponding to a non-touch ofpiezoelectric acoustic resonator 1605, and resonant frequency 320, e.g.,corresponding to a touch of piezoelectric acoustic resonator 1605. Inthis regard, in response to determining that the resonant frequency ofpiezoelectric acoustic resonator 1605 has increased, e.g., to resonantfrequency 1720, control component 1502 can determine that MEMSpiezoelectric acoustic resonator 1605 has been touched, e.g., by a ridgeof a finger.

FIG. 18 illustrates a block diagram of a cross section a MEMSpiezoelectric acoustic resonator including material 1810, in accordancewith various embodiments. As illustrated by FIG. 18, cavity 1640 can befilled with material 1810, e.g., rubber, gel, etc. that is associatedwith a first acoustic velocity that is different from a second acousticvelocity corresponding to substrate 1650. In this regard, a resonantfrequency of MEMS piezoelectric acoustic resonator 1605 can be modifiedin a predetermined manner by selecting material 1810 of a predeterminedacoustic velocity with respect to an acoustic velocity of substrate1650. Further, including material 1810 in cavity 1640 can preventdebris, contaminants, etc. from entering cavity 1640 and subsequentlyintroducing errors in measurements of the resonant frequency of MEMSpiezoelectric acoustic resonator 1605.

FIG. 19 illustrates a block diagram of a cross section of a portion ofan array (1920) of MEMS piezoelectric acoustic resonators (1605) beingcontacted by finger 1910, in accordance with various embodiments.Control component 1502 can determine that finger ridge 1932 has toucheda MEMS piezoelectric acoustic resonator (1605) of the portion of thearray based on a determination that a resonant frequency of the MEMSpiezoelectric acoustic resonator has increased. Further, controlcomponent 1502 can determine that other MEMS piezoelectric acousticresonators (1605) of the portion of the array have not been touched,e.g., by finger ridge 1930 and finger ridge 1934, based on respectivedeterminations that resonant frequencies of the other MEMS piezoelectricacoustic resonators has not changed. In this regard, control component1502 can derive, based on such determinations, a fingerprintcorresponding to finger 510.

Now referring to FIG. 20, a block diagram of a cross section of MEMSpiezoelectric acoustic resonator 2005 is illustrated, in accordance withvarious embodiments. MEMS piezoelectric acoustic resonator 2005, e.g., amembrane resonator, includes cavity 2010 that has been formed by,within, etc. substrate 1650, e.g., a silicon based material, and hasbeen enclosed by bottom electrode 1630 of piezoelectric transducer 1607.Control component 1502 can generate and apply a stimulus, e.g., a pulsesignal, a frequency sweep, an alternating AC voltage, an AC current,etc. to piezoelectric transducer 1607 via top electrode 1610 and bottomelectrode 1630.

As illustrated by FIG. 21, control component 1502 can measure, based onthe stimulus, Q factor 2110, e.g., corresponding to a non-touch ofpiezoelectric acoustic resonator 2005, and Q factor 2120, e.g.,corresponding to a touch of piezoelectric acoustic resonator 2005. Inthis regard, in response to determining that the Q factor ofpiezoelectric acoustic resonator 2005 has decreased, e.g., to Q factor2120, control component 1502 can determine that MEMS piezoelectricacoustic resonator 2005 has been touched, e.g., by a ridge of a finger.

FIG. 22 illustrates a block diagram of a cross section of a portion ofan array (2220) of MEMS piezoelectric acoustic resonators (2005) beingcontacted by finger 1910, in accordance with various embodiments.Control component 1502 can determine that finger ridge 1932 has toucheda MEMS piezoelectric acoustic resonator (2005) of the portion of thearray based on a determination that a Q factor of the MEMS piezoelectricacoustic resonator has decreased. Further, control component 1502 candetermine that other MEMS piezoelectric acoustic resonators (2005) ofthe portion of the array have not been touched, e.g., by finger ridge1930 and finger ridge 1934, based on respective determinations that Qfactors of the other MEMS piezoelectric acoustic resonators have notchanged. In this regard, control component 1502 can derive, based onsuch determinations, a fingerprint corresponding to finger 1910.

In an embodiment illustrated by FIG. 23, top electrode 1610 can form asquare shape that can be smaller, and located above, a square shape ofbottom electrode 1630. In yet another embodiment illustrated by FIG. 24,top electrode 1610 can form a shape of a regular polygon that can besmaller, and located above, a regular polygon shape of bottom electrode1630. In this regard, it should be appreciated by a person of ordinaryskill in MEMS technologies having the benefit of the instant disclosurethat embodiments of devices disclosed herein can comprise electrodes ofvarious shapes. As a non-limiting example, FIG. 29 provides furthershapes and configurations of exemplary PMUT arrays having high fillfactor, in accordance with further non-limiting embodiments.

Referring now to FIG. 25, a block diagram (2500) representing a methodfor manufacturing, assembling, etc. a MEMS piezoelectric acousticresonator, e.g., MEMS piezoelectric acoustic resonator 1605, isillustrated, in accordance with various embodiments. At 1120, an arrayof piezoelectric transducers (1607) can be formed on substrate 2510. Forexample, bottom electrodes (1630) can be formed on substrate 2510;dielectric material 1620 can be formed on, placed on, etc. the bottomelectrodes; and top electrodes (1610) can be formed on, placed on, etc.dielectric material 1620.

At 2530, portions(s) of an array of cavities (1640) can be formed onsubstrate 1650. At 2540, the portion(s) of the array of cavities can beplaced on, attached to, etc. the array of piezoelectric transducers(1607). In another embodiment (not shown), one or more cavities of thearray of cavities can be filled with a material having a first acousticvelocity that is different from a second acoustic velocity of substrate1650. At 2550, substrate 2510 can be removed from the bottom electrodes.

FIG. 26 illustrates a block diagram (2600) representing another methodfor manufacturing, assembling, etc. a MEMS piezoelectric acousticresonator, e.g., MEMS piezoelectric acoustic resonator 2005, isillustrated, in accordance with various embodiments. At 2610, an arrayof piezoelectric transducers (1607) can be formed on substrate 2610. Forexample, top electrodes can be formed on substrate 2610; dielectricmaterial 1620 can be formed on, placed on, etc. the top electrodes andsubstrate 2610; and bottom electrodes (2630) can be formed on, placedon, etc. dielectric material 1620.

At 2620, portions(s) of an array of cavities (2010) can be formed onsubstrate 1650. At 2630, the portion(s) of the array of cavities can beplaced on, attached to, etc. the array of piezoelectric transducers(1607). At 2640, substrate 2610 can be removed from dielectric material1620 and the top electrodes.

The order in which some or all of the manufacturing, assembling, etc.steps described above with respect to block diagrams 2500 and 2600should not be deemed limiting. Rather, it should be understood by aperson of ordinary skill in MEMS technologies having the benefit of theinstant disclosure that some of the steps can be executed in a varietyof orders not illustrated.

In addition to the foregoing, the subject application further describesPMUTs for fingerprint sensing. As described above, MUT devices, as analternative method for fingerprint detection typically require MUTdevices to be manufactured in the resolution of at least 300 dpi orhigher e.g., approximately 85 μm pixel size. In addition, for mobileapplications, optical method can be too bulky or expensive; thermal andcapacitive sensing swipe-based method are not the favored due to userexperience. As area-based fingerprint sensor is convenient in usage, itis suitable for adoption in mobile devices and can provide a sufficientlevel of security. Moreover, ultrasonic fingerprint detection canovercome deficiencies associated with skin condition and/or sensorcontamination that afflict the accuracy of fingerprint detection devicesemploying CMUT linear arrays. For example, existing fingerprint sensorsare mostly based on capacitive sensing. Their detection ability isreadily compromised by excessively dry or wet fingerprints and/orcontamination from sweat or oil. Ultrasonic detection does not rely onelectrical property, instead, it relies on physical contact and acousticimpedance difference and is proven to be able to detect ridges andvalleys and also sweat pores which are not so easily detectable withcapacitive sensing.

Various embodiments disclosed herein provide integrated PMUTs on IC forfingerprint sensing. Additionally, various embodiments can provide anefficient way of creating electrical coupling and mechanical anchoringof ultrasonic transducer pMUT directly on CMOS for reduced parasiticsand fully utilize the routing capability on CMOS metal layers.

In addition, in order to achieve a compact PMUT array with goodresolution, it is desirable to achieve a high fill factor for a PMUTarray that can provide a desired output pressure for the ultrasoundtransducer array. Various embodiments described herein can thus increasethe increase the signal to noise ratio (SNR) of PMUT arrays duringdetection and the array gain, which is the ratio of the array's outputpressure to that of a single PMUT device. However, increasing fillfactor can suppress mechanical coupling between adjacent PMUT pixels.Thus, to achieve proper mechanical coupling or anchor while achieving ahigh fill factor, it is desired to minimize the anchor occupation ratiocompared to the PMUT “active” area. Thus, various embodiments disclosedherein provide integrated PMUTs on IC for fingerprint sensing where thePMUT structures and the array of PMUT structures are configured in arhombus configuration, a hexagonal configuration, and/or a combinationof rhombus configuration and hexagonal configuration.

For example, FIG. 27 depicts a cross-section of an exemplary PMUT 2700for fingerprint sensing, in accordance with various embodiments. As anon-limiting example, exemplary PMUT 2700 can comprise an engineeredsilicon-on-insulator (ESOI) wafer that can comprise a SOI wafer with oneor more cavities beneath the silicon device layer or substrate. Forinstance, exemplary PMUT 2700 can comprise cavity 2702 in PMUTwafer/layer/substrate 2704, to which a silicon dioxide layer/substrate2706 can be deposited on PMUT wafer/layer/substrate 2704 therebyoverlaying PMUT wafer/layer/substrate 2704. Disposed and/or depositedover silicon dioxide layer/substrate 2706 and/or fusion bonded to thesilicon dioxide layer/substrate 2706 can be a substrate/layer formed ofsilicon 2708 or silicon structural substrate/layer 2708. As describedabove regarding FIGS. 9A-9K, for example, the PMUT wafer/layer/substrate2704 inclusive of one or more formed cavity 902 and silicon dioxidelayer/substrate 2706 can be referred to as an engineered substrate, andfor purposes of this disclosure can be referred to as MEMS handle layer.

FIG. 27 further depicts, in inset 2709, exemplary PMUT 2700 furthercomprising successively deposited exemplary aluminum nitride (AlN) seedlayer 2710, molybdenum (Mo) layer 2712, and AlN stacking layer 2714,upon which silicon dioxide standoffs 2716 can be formed to prepare amovable space of exemplary PMUT 2700. The additional deposited ordisposed layers comprising the aluminum nitride seed layer 2710,molybdenum layer 2712, aluminum nitride stacking layer 2714 and silicondioxide standoffs 2716 over substrate/layer formed of silicon 2708 canbe referred to as PMUT device layer/wafer/substrate and/or piezoelectriclayer/wafer/substrate.

Substrate/layer formed of silicon 2708 can be the silicon structurallayer of the PMUT device layer to which the MEMS handle layer (e.g.,PMUT wafer/layer/substrate 2704 inclusive of cavities 2702 and silicondioxide layer/substrate 2706) can have been fusion bonded to the PMUTdevice layer/wafer/substrate (e.g., silicon structural substrate/layer2708, aluminum nitride seed layer 2710, molybdenum layer 2712, aluminumnitride stacking layer 2714, and standoffs 2716). It should be notedthat, if fusion bonded to the PMUT device layer, the fusion bonding ofthe MEMS handle layer to the PMUT device layer can comprise the MEMShandle layer being oxidized and the silicon structural layer/substrate2708 of the PMUT device layer being ground and polished to a target ordefined thickness prior to deposition of the aluminum nitride seed layer2710, molybdenum layer 2712, aluminum nitride stacking layer 2714, andstandoffs 2716 formed of silicon dioxide. Standoffs 2716 are typicallyformed on the PMUT device layer to provide separation between the MEMSstructure and a CMOS wafer/layer/substrate, for example, as depicted inFIG. 28.

FIG. 27 further depicts exemplary PMUT 2700 further comprisingstructures defined for one or more bottom electrodes 2720 that can becarved out by first disposing or depositing a silicon dioxide hard mask(not shown) over the aluminum nitride stacking layer 2714 and standoffs2716 and thereafter etching through silicon dioxide hard mask (notshown) to define the structure and carve out one or more bottomelectrodes 2720, for example, as described above regarding FIGS. 9A-9K,for example. As can be understood, the etching process can etch throughlayers/substrates respectively formed of silicon dioxide hard mask (notshown), aluminum nitride stacking layer 2714, and molybdenum layer 2712.

One or more bottom electrode 2720 contacts 2722 can be created, asdepicted in FIG. 27. In addition, an opening etch on silicon dioxidehard mask (not shown) can be performed to define aluminum top electrode2724 contacts, thus forming electrical contacts to the molybdenum layer2712 and aluminum nitride stacking layer 2714. The defined structure andcarved out one or more bottom electrodes 2720, the bottom electrode 2720contact 2722, and the aluminum top electrode 2724 contacts, as depictedin FIG. 27, can be undertaken by patterning the aluminum or othersuitable material through a silicon dioxide hard mark (not shown).

In addition, aluminum and titanium layers (not shown) can be depositedfor the purposes of top electrode material deposition and then germaniumlayers 2728 can be deposited over the aluminum and titanium (not shown)so that pads and electrodes can be patterned, as described aboveregarding FIGS. 9A-9K, for example, as well as forming a barrier layerand eutectic bonding layer.

FIG. 28 depicts a cross-section 2800 of exemplary PMUT 2700 forfingerprint sensing on IC comprising exemplary PMUT 2700 bonded to anexemplary CMOS wafer 2802, in accordance with further non-limitingembodiments. For example, an exemplary CMOS wafer 2802 can compriseexemplary source/drain regions 2804, gate 2806, one or more vias 2808,and one or more metal layers including a first metal layer 2810 and anexemplary top metal layer 2812. In a non-limiting aspect, an exemplarytop metal layer 2812 of exemplary CMOS wafer 2802 can comprise aluminum.

Thus, as described above regarding FIG. 9J, for example, exemplary CMOSwafer 2802 and exemplary PMUT 2700 can be bonded using analuminum-germanium eutectic bond between exemplary top metal layer 2812of exemplary CMOS wafer 2802 and germanium layers 2728 on standoffs 2716of exemplary PMUT 2700. The Aluminum-Germanium eutectic bond can createa hermetic seal around desired MEMS structures and/or CMOS wafer 2802circuits and form a bonded wafer comprising exemplary CMOS wafer 2802and exemplary PMUT 2700. As can be understood the single bonding processusing an Aluminum-Germanium eutectic bond provides hermetic sealing,mechanical anchoring, and electrical connection in one step. Theeutectically bonded wafer comprising exemplary CMOS wafer 2802 andexemplary PMUT 2700 can then be thinned, for instance, on the PMUTwafer/layer/substrate 2704 side, to a defined or desired thickness. Inaddition, a port or cavity (e.g., cavity 2702 or other) can be formed ona polished side of the PMUT wafer/layer/substrate 2704 to create accessto the surrounding environment, as describe above regarding FIG. 9K, forexample. For instance, an etch can be performed on the top side of thebonded wafer to form an acoustic port or cavity for sound propagation.

As described above, achieving high fill factor for a PMUT array canprovide a desired output pressure for the ultrasound transducer array,increasing the PMUT array gain. However, increasing fill factor cansuppress mechanical coupling between adjacent PMUT pixels. Thus, toachieve proper mechanical coupling or anchor while achieving a high fillfactor is desired to minimize the anchor occupation ratio compared tothe PMUT “active” area. Thus, various embodiments disclosed hereinprovide integrated PMUTs on IC for fingerprint sensing where the PMUTstructures and the array of PMUT structures are configured in a rhombusconfiguration, a hexagonal configuration, and/or a combination ofrhombus configuration and hexagonal configuration.

Accordingly, FIG. 29 depicts cross-sections of exemplary PMUT arrays(2902, 2904, 2906) having high fill factor, in accordance with furthernon-limiting embodiments. As non-limiting examples, FIG. 29 depictsexemplary PMUT arrays (2902, 2904, 2906) comprising PMUT structures inthe exemplary PMUT arrays (2902, 2904, 2906) of PMUT structures that areconfigured in a rhombus configuration (2908, 2910) or a hexagonalconfiguration (2912, 2914). As depicted in FIG. 29, the exemplary PMUTarrays (2902) of PMUT structures can comprise PMUT structures that areconfigured in a rhombus configuration (2908), the exemplary PMUT arrays(2904) of PMUT structures can comprise PMUT structures that areconfigured in a hexagonal configuration (2912), or the exemplary PMUTarrays (2906) of PMUT structures can comprise PMUT structures that areconfigured in a combination of rhombus configuration (2910) andhexagonal configuration (2914) arranged as a unit cell.

Note that, according to a non-limiting aspect, edges of the PMUTstructures between neighboring PMUT structures of the exemplary PMUTarrays (2902, 2904, 2906) can correspond to mechanical anchor 2918points for the PMUT structure, for example, such as provided byaluminum-germanium eutectic bond between exemplary top metal layer 2812of exemplary CMOS wafer 2802 and germanium layers 2728 on standoffs 2716of exemplary PMUT 2700, as described above, regarding FIG. 27, forexample. As described above, to achieve proper mechanical coupling ormechanical anchor 2918 while achieving a high fill factor, it is desiredto minimize the anchor occupation ratio compared to the PMUT structureactive area 2920. Exemplary PMUT arrays (2902, 2904, 2906), as describedherein, can provide high fill factor, thus increasing the array gain ofexemplary PMUT arrays (2902, 2904, 2906).

In another non-limiting aspect, exemplary PMUT arrays (2902) of PMUTstructures comprising PMUT structures configured in a hexagonalconfiguration (2912) can be formed in quadrilateral shape having anglesof about 60 degrees. In a further non-limiting aspect, exemplary PMUTarrays (2904) of PMUT structures comprising PMUT structures configuredin a rhombus configuration (2908) can be formed in quadrilateral shapehaving angles of about 60 degrees and about 120 degrees.

While the foregoing can provide exemplary PMUTs on IC for fingerprintsensing comprising compact PMUT arrays with good resolution, siliconfabrication cost of exemplary PMUT 2700 bonded to an exemplary CMOSwafer 2802, as described above regarding FIG. 28, can be improved, forexample, by integrating exemplary PMUTs on IC (e.g., an exemplary CMOSwafer) for fingerprint sensing. Accordingly, FIG. 30 depicts across-section of exemplary PMUT for fingerprint sensing on IC comprisingexemplary PMUT 3000 integrated on an exemplary CMOS wafer, in accordancewith further non-limiting embodiments. As a non-limiting example, anexemplary PMUT 3000 can be integrated on an exemplary CMOS wafer, asdescribed below regarding FIGS. 31-45.

For example, FIG. 31 depicts a cross-section 3100 of an exemplary CMOSwafer 3102 suitable for incorporation of aspects of the subjectdisclosure directed to fabrication of exemplary PMUT and PMUT arrays forfingerprint sensing on IC comprising exemplary one or more exemplaryPMUTs integrated on exemplary CMOS wafer 3102, in accordance withfurther non-limiting embodiments. As a non-limiting example, exemplaryCMOS wafer 3102 can comprise exemplary source/drain regions 3104, gate3106, one or more vias 3108, and one or more metal layers including afirst metal layer 3110 and an exemplary top metal layer 3112. In anon-limiting aspect, an exemplary top metal layer 3112 of exemplary CMOSwafer 3102 can comprise aluminum. In addition, exemplary CMOS wafer 3102can comprise an exemplary silicon dioxide layer 3114 disposed over theexemplary top metal layer 3112 and an exemplary passivation layer 3116disposed over the exemplary silicon dioxide layer 3114.

FIG. 32 depicts a cross-section 3200 of an exemplary CMOS wafer 3102comprising one or more exemplary cavities 3202, in accordance withfurther aspects described herein directed to a non-limiting cavitydeposition etch process. As a non-limiting example, exemplarypassivation layer 3116 and exemplary silicon dioxide layer 3114 can beetched in a desired pattern with a timed etch is then performed tocreate the one or more exemplary cavities 3202. In a furthernon-limiting aspect, the one or more exemplary cavities 3202 can becreated by employing a timed etch, resulting in an exemplary cavitydepth of less than 0.8 μm (+/−10%).

FIG. 33 depicts a cross-section 3300 of an exemplary CMOS wafer 3102comprising one or more exemplary sacrificial materials 3302, inaccordance with further aspects described herein directed tonon-limiting amorphous silicon deposition and subsequentchemical-mechanical planarizing processes. As a non-limiting example,one or more exemplary sacrificial materials 3302, e.g., such asamorphous silicon, etc. can be deposited in the one or more exemplarycavities 3202. In a non-limiting aspect, the one or more exemplarysacrificial materials 3302 can comprise amorphous silicon. In a furthernon-limiting aspect, the one or more exemplary sacrificial materials3302 can comprise silicon-germanium (SiGe) or tungsten (W), whichincluding amorphous silicon are all CMOS foundry compatible materialsand can be removed with xenon difluoride (XeF₂) or sulfur hexafluoride(SF₆). In another non-limiting aspect, exemplary CMOS wafer 3102comprising one or more exemplary sacrificial materials 3302 can bepolished (e.g., chemical-mechanical planarizing) to planarize thesurface, resulting in a sacrificial material film thickness of aboutless than 0.8 μm to prevent cracking and peeling of the sacrificialmaterial film.

FIG. 34 depicts a cross-section 3400 of an exemplary CMOS wafer 3102comprising one or more exemplary silicon dioxide (SiO₂) layers 3402, inaccordance with further aspects described herein directed to anon-limiting silicon dioxide deposition process. As a non-limitingexample, one or more exemplary silicon dioxide (SiO₂) layers 3402 can bedeposited to cover the surface of the exemplary CMOS wafer 3102comprising one or more exemplary sacrificial materials 3302 and serve asa structure material in the fabrication of one or more exemplary PMUTsintegrated on exemplary CMOS wafer 3102, in accordance with furthernon-limiting embodiments.

FIG. 35 depicts a cross-section 3500 of an exemplary CMOS wafer 3102comprising one or more exemplary seal holes 3502, in accordance withfurther aspects described herein directed to a non-limiting release holeopening process. Accordingly, in a further non-limiting aspect,exemplary CMOS wafer 3102 comprising one or more exemplary silicondioxide (SiO₂) layers 3402 can be etched to create one or more sealholes. In another non-limiting aspect, for example, as depicted inset3504, a seal hole profile having an aspect ratio greater than 4 canfacilitate providing adequate sealing of the one or more exemplarycavities 3202. In addition, in a further non-limiting aspect, layout forthe one or more exemplary cavities 3202 and one or more exemplary sealholes 3502 can comprise the one or more exemplary seal holes 3502 placedat the respective edges of the one or more exemplary cavities 3202, suchthat sealing of the one or more exemplary seal holes 3502 does notcreate an obstruction if the area in the one or more exemplary cavities3202 directly underneath the one or more exemplary seal holes 3502 isfully filled, for example, as depicted in FIG. 35.

FIG. 36 depicts a cross-section 3600 of an exemplary CMOS wafer 3102comprising one or more exemplary cavities 3202, in accordance withfurther aspects described herein directed to a non-limiting release etchprocess. Accordingly, in a further non-limiting aspect, exemplary CMOSwafer 3102 comprising the one or more exemplary seal holes 3502 and oneor more exemplary sacrificial materials 3302 can be exposed to asacrificial release etch to remove the one or more exemplary sacrificialmaterials 3302 (e.g., amorphous silicon, etc.). In a non-limitingaspect, exemplary CMOS wafer 3102 comprising the one or more exemplaryseal holes 3502 and one or more exemplary sacrificial materials 3302 canbe exposed to a sacrificial release etch employing either a dry etch ora wet etch. As a non-limiting example, an exemplary dry etch can employXeF2 or SF6 as etching gas. In a further non-limiting example, anexemplary wet etch can employ poly-etch (e.g., H:N:A, or a solution ofHydrofluoric Acid (HF):Nitric Acid (HNO₃):Acetic acid (CH₃COOH) in adesired ratio), potassium hydroxide (KOH) or tetramethyl ammoniumhydroxide (TMAH), with care taken to prevent stiction of the membranecreated from the one or more exemplary silicon dioxide (SiO₂) layers3402. The one or more exemplary sacrificial materials 3302 thus removed,FIG. 36 depicts exemplary CMOS wafer 3102 comprising one or moreexemplary cavities 3202 and one or more exemplary unsealed seal holes3602, for example, in inset 3604.

FIG. 37 depicts a cross-section 3700 of an exemplary CMOS wafer 3102comprising one or more exemplary seal hole seals 3702, in accordancewith further aspects described herein directed to non-limiting sealdeposition and etch back processes. As a non-limiting example, exemplaryCMOS wafer 3102 comprising one or more exemplary cavities 3202 and oneor more exemplary unsealed seal holes 3602 can be exposed to aplasma-enhanced chemical vapor deposition (PECVD) process for SiO₂deposition to create the one or more exemplary seal hole seals 3702 asdepicted in inset 3704. As can be understood, the PECVD of SiO₂ cancreate additional thickness of silicon dioxide which can be subject toan etch back process to control the final structure membrane thickness.It is further noted that, SiO₂ is defect tolerable for subsequent AlNdeposition.

FIG. 38 depicts a cross-section 3800 of an exemplary CMOS wafer 3102, ininset 3802, for example, comprising an exemplary aluminum nitride (AlN)seed layer 3804, molybdenum (Mo) layer 3806, and AlN stacking layer3808, in accordance with further aspects described herein directed tonon-limiting AlN Seed/Mo/AlN deposition processes, for example, asfurther describe above regarding FIGS. 9A-9K, 27, etc.

One or more exemplary bottom contacts 4002 to molybdenum (Mo) layer 3806and one or more exemplary vias 4102 contact to exemplary top metal layer3112 of exemplary CMOS wafer 3102 can then be created by employing ahard mask on top of AlN stacking layer 3808. Thus, FIG. 39 depicts across-section 3900 of an exemplary CMOS wafer 3102 comprising one ormore exemplary SiO₂ layers 3902, in accordance with further aspectsdescribed herein directed to a non-limiting hard mask depositionprocess. In addition, FIG. 40 depicts a cross-section 4000 of anexemplary CMOS wafer 3102, in inset 4004 comprising one or moreexemplary bottom contacts 4002, in accordance with further aspectsdescribed herein directed to a non-limiting bottom contact to molybdenumfabrication process. In a non-limiting aspect, in addition to etchingone or more exemplary bottom contacts 4002 to molybdenum (Mo) layer3806, areas comprising AlN (e.g., selected areas of AlN stacking layer3808) over the one or more exemplary vias 4102 contact to exemplary topmetal layer 3112 can also be etched to reduce etch difficulty infabricating the one or more exemplary vias 4102 contact to exemplary topmetal layer 3112. Thus, FIG. 41 depicts a cross-section 4100 of anexemplary CMOS wafer comprising 3102 one or more exemplary vias 4102, inaccordance with further aspects described herein directed to anon-limiting wafer via etch process. Subsequently, the hard maskcomprising one or more exemplary SiO₂ layers 3902 can be removed asshown in FIG. 42, which depicts a cross-section 4200 of an exemplaryCMOS wafer 3102 comprising an exposed AlN surface 4202 (e.g., AlNstacking layer 3808), in accordance with further aspects describedherein directed to a non-limiting hard mask removal process.

FIG. 43 depicts a cross-section of an exemplary CMOS wafer comprisingone or more exemplary SiO₂ spacers 4302, in accordance with furtheraspects described herein directed to a non-limiting SiO₂ spacerfabrication process. As a non-limiting example, a layer of SiO₂ (notshown) can be deposited and blank etched (e.g., without a mask materialsuch as a photo resistive layer described above) to remove the topsurface oxide completely while preserving the one or more exemplary SiO₂spacers 4302. FIG. 44 depicts a cross-section 4400 of an exemplary CMOSwafer 3102 comprising one or more exemplary top electrodes 4402, inaccordance with further aspects described herein directed to anon-limiting top electrode fabrication process. As a non-limitingexample, one or more exemplary top electrodes 4402 material (e.g.,aluminum, etc.) can be deposited and patterned to form the one or moreexemplary top electrodes 4402 for exemplary PMUT and PMUT arrays and toform electrical connection to exemplary top metal layer 3112 ofexemplary CMOS wafer 3102. As can be seen FIGS. 43-44, preserving theone or more exemplary SiO₂ spacers 4302 can prevent shorting of the oneor more exemplary top electrodes 4402 and the one or more exemplarybottom contacts 4002 to the bottom electrode and exemplary aluminumnitride (AlN) seed layer 3804.

FIG. 45 depicts exemplary PMUT for fingerprint sensing on IC comprisingexemplary PMUT 3000 integrated on exemplary CMOS wafer 3102 as describedabove regarding FIGS. 30-44, for which exemplary CMOS 3102 wafercomprises one or more exemplary passivation layers 4502, in accordancewith further aspects described herein directed to a non-limitingpassivation process. As a non-limiting example, one or more exemplarypassivation layers 4502 can be deposited on exemplary CMOS 3102 waferand patterned to open one or more wire bond pads 4504 and/or one or morevias 4506 of exemplary PMUT 3000 integrated on exemplary CMOS wafer3102. As described above, inset 4508 depicts various non-limitingaspects of exemplary PMUT 3000 integrated on exemplary CMOS wafer 3102,for example, as described above regarding FIGS. 31-45.

Accordingly, various non-limiting embodiments of the subject disclosurecan comprise an exemplary MEMS device (e.g., exemplary PMUT 2700 forfingerprint sensing on IC comprising exemplary PMUT 2700 bonded to anexemplary CMOS wafer 2802, exemplary PMUT 3000 integrated on exemplaryCMOS wafer 3102, etc.), comprising a MUT structure (e.g., exemplary PMUT2700 or portions thereof, exemplary PMUT 3000 or portions thereof, etc.)and a piezoelectric material (e.g., one or more of aluminum nitride,lead zirconate titanate (PZT), zinc oxide, polyvinylidene difluoride(PVDF), lithium niobate (LiNbO3)) disposed within the MEMS device (e.g.,exemplary PMUT 2700 for fingerprint sensing on IC comprising exemplaryPMUT 2700 bonded to an exemplary CMOS wafer 2802, exemplary PMUT 3000integrated on exemplary CMOS wafer 3102, etc.) comprising a PMUT arrayof a fingerprint sensor adapted to sense a characteristic of afingerprint placed adjacent to the MUT structure.

Further non-limiting embodiments of the subject disclosure can comprisean exemplary MEMS device (e.g., exemplary PMUT 3000 integrated onexemplary CMOS wafer 3102, etc.) comprising a MUT structure (e.g.,exemplary PMUT 3000 or portions thereof, etc.) formed integrally to theCMOS structure (e.g., exemplary CMOS wafer 3102 or portions thereof,etc.) having a plurality of cavities (e.g., one or more exemplarycavities 3202, etc.) formed within the CMOS structure and thepiezoelectric material (e.g., one or more of aluminum nitride, leadzirconate titanate (PZT), zinc oxide, polyvinylidene difluoride (PVDF),lithium niobate (LiNbO3)) disposed on the CMOS structure.

In a non-limiting aspect, exemplary MEMS device (e.g., exemplary PMUT2700 for fingerprint sensing on IC comprising exemplary PMUT 2700 bondedto an exemplary CMOS wafer 2802, exemplary PMUT 3000 integrated onexemplary CMOS wafer 3102, etc.) can further comprise a first metalconductive layer (e.g., such as described regarding aluminum topelectrode 2724, regarding one or more exemplary top electrodes 4402,etc., in reference to FIGS. 27 and 44) disposed on the piezoelectricmaterial (e.g., one or more of aluminum nitride, lead zirconate titanate(PZT), zinc oxide, polyvinylidene difluoride (PVDF), lithium niobate(LiNbO3)).

In a further non-limiting aspect, exemplary MEMS device (e.g., exemplaryPMUT 2700 for fingerprint sensing on IC comprising exemplary PMUT 2700bonded to an exemplary CMOS wafer 2802, exemplary PMUT 3000 integratedon exemplary CMOS wafer 3102, etc.) can further comprise a plurality ofmetal electrodes (e.g., one or more of aluminum top electrodes 2724, oneor more bottom electrodes 2720, one or more exemplary top electrodes4402, one or more exemplary bottom contacts 4002, etc.) configured toform electrical connections between the first metal conductive layer(e.g., such as described regarding aluminum top electrode 2724,regarding one or more exemplary top electrodes 4402, etc., in referenceto FIGS. 27 and 44), the piezoelectric material (e.g., one or more ofaluminum nitride, lead zirconate titanate (PZT), zinc oxide,polyvinylidene difluoride (PVDF), lithium niobate (LiNbO3)), and a CMOSstructure (e.g., exemplary CMOS wafer 2802 or portions thereof,exemplary CMOS wafer 3102 or portions thereof, etc.), wherein the pMUTstructure and the CMOS structure are vertically stacked, for example, asdepicted in FIGS. 28, 45, etc.

In a further non-limiting aspect, exemplary MEMS device (e.g., exemplaryPMUT 2700 for fingerprint sensing on IC comprising exemplary PMUT 2700bonded to an exemplary CMOS wafer 2802, exemplary PMUT 3000 integratedon exemplary CMOS wafer 3102, etc.) can further comprise a second metalconductive layer (e.g., molybdenum (Mo) layer 2712, molybdenum (Mo)layer 3806, etc.) disposed on the piezoelectric material (e.g., one ormore of aluminum nitride, lead zirconate titanate (PZT), zinc oxide,polyvinylidene difluoride (PVDF), lithium niobate (LiNbO3)) and oppositethe first metal conductive layer. (e.g., such as described regardingaluminum top electrode 2724, regarding one or more exemplary topelectrodes 4402, etc., in reference to FIGS. 27 and 44).

In addition, exemplary MEMS device (e.g., exemplary PMUT 2700 forfingerprint sensing on IC comprising exemplary PMUT 2700 bonded to anexemplary CMOS wafer 2802) can further comprise a stand-off (e.g., oneor more silicon dioxide standoffs 2716, etc.) formed on thepiezoelectric material (e.g., one or more of aluminum nitride, leadzirconate titanate (PZT), zinc oxide, polyvinylidene difluoride (PVDF),lithium niobate (LiNbO3)), according to further non-limiting aspects.For example, an exemplary stand-off (e.g., one or more silicon dioxidestandoffs 2716, etc.) can comprise a silicon dioxide layer depositedover the piezoelectric material. In other non-limiting aspects,exemplary MEMS device (e.g., exemplary PMUT 2700 for fingerprint sensingon IC comprising exemplary PMUT 2700 bonded to an exemplary CMOS wafer2802) can further comprise the MUT structure (e.g., exemplary PMUT 2700or portions thereof, etc.) bonded to the CMOS structure (e.g., exemplaryCMOS wafer 2802 or portions thereof, etc.) at the standoff (e.g., one ormore silicon dioxide standoffs 2716, etc.) via at least one of aeutectic bonding layer (e.g., comprising an aluminum-germanium eutecticbonding layer, etc.), a compression bond, or a conductive epoxy and/orthe MUT structure electrically coupled to the CMOS structure at thestandoff, for example, as further described herein.

In further non-limiting aspect, exemplary MEMS device (e.g., exemplaryPMUT 2700 for fingerprint sensing on IC comprising exemplary PMUT 2700bonded to an exemplary CMOS wafer 2802, exemplary PMUT 3000 integratedon exemplary CMOS wafer 3102, etc.) can further comprise a piezoelectriclayer comprising an aluminum nitride (AlN) seed layer, a bottom metallayer, and an aluminum nitride (AlN) layer, for example, as furtherdescribed herein. In still another non-limiting aspect, exemplary MEMSdevice (e.g., exemplary PMUT 2700 for fingerprint sensing on ICcomprising exemplary PMUT 2700 bonded to an exemplary CMOS wafer 2802,exemplary PMUT 3000 integrated on exemplary CMOS wafer 3102, etc.) canfurther comprise a PMUT array, as described herein, comprising the MUTstructure (e.g., exemplary PMUT 2700 or portions thereof, exemplary PMUT3000 or portions thereof, etc.) in an array of MUT structures (e.g.,exemplary PMUT arrays (2902, 2904, 2906), etc.), wherein the MUTstructure in the array of MUT structures are configured in a rhombusconfiguration (2908), in a hexagonal configuration (2912), and/or anycombination thereof (e.g., exemplary PMUT arrays 2906). As anon-limiting example, an exemplary MUT structure (e.g., exemplary PMUT2700 or portions thereof, exemplary PMUT 3000 or portions thereof, etc.)and the array of MUT structures (e.g., exemplary PMUT arrays 2906, etc.)can comprise a first two of the array of MUT structures in the rhombusconfiguration 2910 and a second two of the array of MUT structures inthe hexagonal configuration 2914 arranged as a unit cell (e.g.,exemplary PMUT arrays 2906, etc.).

As described below, the subject application further describes variousembodiments that can employ scandium doped aluminum nitride in lieu ofaluminum nitride as a piezoelectric material to facilitate improvementsin performance of various disclosed embodiments.

In addition, in further non-limiting embodiments of the subjectdisclosure can comprise an exemplary MEMS device (e.g., exemplary PMUT3000 integrated on exemplary CMOS wafer 3102, etc.), comprising a CMOSdevice wafer (e.g., exemplary CMOS wafer 3102) associated with a PMUTarray of a fingerprint sensor and having a plurality of cavities (e.g.,cavities 3202) configured in an array.

In a non-limiting aspect, exemplary MEMS device (e.g., exemplary PMUT3000 integrated on exemplary CMOS wafer 3102, etc.) can further comprisea first metal conductive layer (e.g., such as described regarding one ormore exemplary top electrodes 4402, etc., in reference to FIG. 44)disposed on the CMOS device wafer (e.g., exemplary CMOS wafer 3102) andover the plurality of cavities (e.g., cavities 3202).

In another non-limiting aspect, exemplary MEMS device (e.g., exemplaryPMUT 3000 integrated on exemplary CMOS wafer 3102, etc.) can furthercomprise a piezoelectric material (e.g., one or more of aluminumnitride, lead zirconate titanate (PZT), zinc oxide, polyvinylidenedifluoride (PVDF), lithium niobate (LiNbO3)) disposed on the first metalconductive layer (e.g., such as described regarding one or moreexemplary top electrodes 4402, etc., in reference to FIG. 44). In stillanother non-limiting aspect, exemplary MEMS device (e.g., exemplary PMUT3000 integrated on exemplary CMOS wafer 3102, etc.) can further compriseone or more bottom electrodes (e.g., one or more exemplary bottomcontacts 4002, etc.) electrically coupled to one or more top electrodes(e.g., one or more exemplary top electrodes 4402, etc.) via thepiezoelectric material. In addition, further non-limiting embodiments ofexemplary MEMS device (e.g., exemplary PMUT 3000 integrated on exemplaryCMOS wafer 3102, etc.) can further comprise an acoustic propagationlayer over the one or more top electrodes (e.g., one or more exemplarytop electrodes 4402, etc.), for example, as further described above, forexample, regarding FIG. 18. As a non-limiting example, an exemplaryacoustic propagation layer comprising a liquid, a polymer, or anacoustic impedance matching material configured to provide acousticimpedance matching between a PMUT device associated with the one or moretop electrodes and the cover layer, can be deposited over the one ormore top electrodes (e.g., one or more exemplary top electrodes 4402,etc.).

In a further non-limiting aspect, exemplary MEMS device (e.g., exemplaryPMUT 3000 integrated on exemplary CMOS wafer 3102, etc.) can furthercomprise a second metal conductive layer (e.g., molybdenum (Mo) layer3806, etc.), disposed on the piezoelectric material (e.g., one or moreof aluminum nitride, lead zirconate titanate (PZT), zinc oxide,polyvinylidene difluoride (PVDF), lithium niobate (LiNbO3)),electrically coupling the second metal conductive layer and one or moreCMOS device wafer electrode (e.g., associated with exemplary top metallayer 3112), and electrically coupling the first metal conductive layer(e.g., such as described regarding one or more exemplary top electrodes4402, etc., in reference to FIG. 44) to one or more other CMOS devicewafer electrode (e.g., associated with exemplary top metal layer 3112),wherein the plurality of cavities (e.g., cavities 3202), thepiezoelectric material, the first metal conductive layer, and the secondmetal conductive layer are configured as a plurality of PMUT structures(e.g., a plurality of exemplary PMUTs 3000, or portions thereof,integrated on exemplary CMOS wafer 3102, etc.).

As a non-limiting example, the plurality of PMUT structures (e.g., aplurality of exemplary PMUTs 3000, or portions thereof, integrated onexemplary CMOS wafer 3102, etc.) can be formed integrally to a CMOSstructure (e.g., exemplary CMOS wafer 3102, or portions thereof, etc.),and wherein the fingerprint sensor is adapted to sense a characteristicof a fingerprint placed adjacent to the PMUT array and opposite theplurality of cavities (e.g., cavities 3202). In a further non-limitingexample, the plurality of PMUT structures (e.g., a plurality ofexemplary PMUTs 3000, or portions thereof, integrated on exemplary CMOSwafer 3102, etc.) can comprise the plurality of PMUT structures in arhombus configuration (2908), in a hexagonal configuration (2912),and/or in any combination thereof (e.g., exemplary PMUT arrays 2906). Asa non-limiting example, an exemplary PMUT structure (e.g., exemplaryPMUT 3000 or portions thereof, etc.) and the plurality of PMUTstructures (e.g., exemplary PMUT arrays 2906, etc.) can comprise a firsttwo of the plurality of PMUT structures in the rhombus configuration2910 and a second two of the plurality of MUT structures in thehexagonal configuration 2914 arranged as a unit cell (e.g., exemplaryPMUT arrays 2906, etc.).

As described above, the subject application further describes variousembodiments that can employ scandium doped aluminum nitride in lieu ofaluminum nitride as a piezoelectric material to facilitate improvementsin performance of various disclosed embodiments. For example, in variousembodiments employing a piezoelectric material, for a given voltage,various embodiments can experience more deflection from a scandium dopedaluminum nitride element compared to an aluminum nitride element of thesame design. Alternatively, a higher signal to noise ratio can beexperienced with a scandium doped aluminum nitride element compared toan aluminum nitride element of the same design, for example, a highercontrast to noise ratio (CNR) in a scandium doped aluminum nitrideelement fingerprint sensor, etc. In a further non-limiting aspect,various embodiments employing scandium doped aluminum nitride element,with its attendant performance improvements, compared to an aluminumnitride element, can facilitate other process or design improvements,such as, reductions in device size or footprint, increased resolution,material, processing cost, and/or processing time reductions, etc.

Thus, in further non-limiting embodiments, a piezoelectric materialcomprising scandium doped aluminum nitride can be deposited onto asubstrate or device wafer. In a non-limiting aspect, sputter depositionsputtering targets comprising about 10-30% scandium doped aluminumnitride can be employed to deposit a piezoelectric material comprisingscandium doped aluminum nitride onto a substrate or device wafer. In afurther non-limiting aspect, sputter deposition sputtering targetscomprising about 20-30% (or greater) scandium doped aluminum nitride canbe employed to deposit a piezoelectric material comprising scandiumdoped aluminum nitride onto a substrate or device wafer. In yet othernon-limiting aspects, embodiments employing a piezoelectric materialcomprising scandium doped aluminum nitride can provide certain benefitsover other piezoelectric material substitutes for aluminum nitride. Forexample, scandium doped aluminum nitride can be preferable to be leadcontrols required by, and costs associated with, a PZT process. As afurther example, process and design changes associated with scandiumdoped aluminum nitride piezoelectric material can be minimal, ascompared other possible substitutions.

Accordingly, various non-limiting embodiments of the subject disclosurecan comprise an exemplary MEMS device (e.g., exemplary PMUT 2700 forfingerprint sensing on IC comprising exemplary PMUT 2700 bonded to anexemplary CMOS wafer 2802, exemplary PMUT 3000 integrated on exemplaryCMOS wafer 3102, etc.), comprising a MUT structure (e.g., exemplary PMUT2700 or portions thereof, exemplary PMUT 3000 or portions thereof, etc.)and a piezoelectric material (e.g., one or more of scandium dopedaluminum nitride, scandium doped aluminum nitride of about 10-30%,scandium doped aluminum nitride of greater than about 30%) disposedwithin the MEMS device (e.g., exemplary PMUT 2700 for fingerprintsensing on IC comprising exemplary PMUT 2700 bonded to an exemplary CMOSwafer 2802, exemplary PMUT 3000 integrated on exemplary CMOS wafer 3102,etc.) comprising a PMUT array of a fingerprint sensor adapted to sense acharacteristic of a fingerprint placed adjacent to the MUT structure.

Further non-limiting embodiments of the subject disclosure can comprisean exemplary MEMS device (e.g., exemplary PMUT 3000 integrated onexemplary CMOS wafer 3102, etc.) comprising a MUT structure (e.g.,exemplary PMUT 3000 or portions thereof, etc.) formed integrally to theCMOS structure (e.g., exemplary CMOS wafer 3102 or portions thereof,etc.) having a plurality of cavities (e.g., one or more exemplarycavities 3202, etc.) formed within the CMOS structure and thepiezoelectric material (e.g., one or more of scandium doped aluminumnitride, scandium doped aluminum nitride of about 10-30%, scandium dopedaluminum nitride of greater than about 30%) disposed on the CMOSstructure.

In a non-limiting aspect, exemplary MEMS device (e.g., exemplary PMUT2700 for fingerprint sensing on IC comprising exemplary PMUT 2700 bondedto an exemplary CMOS wafer 2802, exemplary PMUT 3000 integrated onexemplary CMOS wafer 3102, etc.) can further comprise a first metalconductive layer (e.g., such as described regarding aluminum topelectrode 2724, regarding one or more exemplary top electrodes 4402,etc., in reference to FIGS. 27 and 44) disposed on the piezoelectricmaterial (e.g., one or more of scandium doped aluminum nitride, scandiumdoped aluminum nitride of about 10-30%, scandium doped aluminum nitrideof greater than about 30%).

In a further non-limiting aspect, exemplary MEMS device (e.g., exemplaryPMUT 2700 for fingerprint sensing on IC comprising exemplary PMUT 2700bonded to an exemplary CMOS wafer 2802, exemplary PMUT 3000 integratedon exemplary CMOS wafer 3102, etc.) can further comprise a plurality ofmetal electrodes (e.g., one or more of aluminum top electrodes 2724, oneor more bottom electrodes 2720, one or more exemplary top electrodes4402, one or more exemplary bottom contacts 4002, etc.) configured toform electrical connections between the first metal conductive layer(e.g., such as described regarding aluminum top electrode 2724,regarding one or more exemplary top electrodes 4402, etc., in referenceto FIGS. 27 and 44), the piezoelectric material (e.g., one or more ofscandium doped aluminum nitride, scandium doped aluminum nitride ofabout 10-30%, scandium doped aluminum nitride of greater than about30%), and a CMOS structure (e.g., exemplary CMOS wafer 2802 or portionsthereof, exemplary CMOS wafer 3102 or portions thereof, etc.), whereinthe pMUT structure and the CMOS structure are vertically stacked, forexample, as depicted in FIGS. 28, 45, etc.

In a further non-limiting aspect, exemplary MEMS device (e.g., exemplaryPMUT 2700 for fingerprint sensing on IC comprising exemplary PMUT 2700bonded to an exemplary CMOS wafer 2802, exemplary PMUT 3000 integratedon exemplary CMOS wafer 3102, etc.) can further comprise a second metalconductive layer (e.g., molybdenum (Mo) layer 2712, molybdenum (Mo)layer 3806, etc.) disposed on the piezoelectric material (e.g., one ormore of scandium doped aluminum nitride, scandium doped aluminum nitrideof about 10-30%, scandium doped aluminum nitride of greater than about30%) and opposite the first metal conductive layer. (e.g., such asdescribed regarding aluminum top electrode 2724, regarding one or moreexemplary top electrodes 4402, etc., in reference to FIGS. 27 and 44).

In addition, exemplary MEMS device (e.g., exemplary PMUT 2700 forfingerprint sensing on IC comprising exemplary PMUT 2700 bonded to anexemplary CMOS wafer 2802) can further comprise a stand-off (e.g., oneor more silicon dioxide standoffs 2716, etc.) formed on thepiezoelectric material (e.g., one or more of scandium doped aluminumnitride, scandium doped aluminum nitride of about 10-30%, scandium dopedaluminum nitride of greater than about 30%), according to furthernon-limiting aspects. For example, an exemplary stand-off (e.g., one ormore silicon dioxide standoffs 2716, etc.) can comprise a silicondioxide layer deposited over the piezoelectric material. In othernon-limiting aspects, exemplary MEMS device (e.g., exemplary PMUT 2700for fingerprint sensing on IC comprising exemplary PMUT 2700 bonded toan exemplary CMOS wafer 2802) can further comprise the MUT structure(e.g., exemplary PMUT 2700 or portions thereof, etc.) bonded to the CMOSstructure (e.g., exemplary CMOS wafer 2802 or portions thereof, etc.) atthe standoff (e.g., one or more silicon dioxide standoffs 2716, etc.)via at least one of a eutectic bonding layer (e.g., comprising analuminum-germanium eutectic bonding layer, etc.), a compression bond, ora conductive epoxy and/or the MUT structure electrically coupled to theCMOS structure at the standoff, for example, as further describedherein.

In further non-limiting aspect, exemplary MEMS device (e.g., exemplaryPMUT 2700 for fingerprint sensing on IC comprising exemplary PMUT 2700bonded to an exemplary CMOS wafer 2802, exemplary PMUT 3000 integratedon exemplary CMOS wafer 3102, etc.) can further comprise a piezoelectriclayer comprising an aluminum nitride (AlN) seed layer, a bottom metallayer, and an aluminum nitride (AlN) layer, for example, as furtherdescribed herein. In still another non-limiting aspect, exemplary MEMSdevice (e.g., exemplary PMUT 2700 for fingerprint sensing on ICcomprising exemplary PMUT 2700 bonded to an exemplary CMOS wafer 2802,exemplary PMUT 3000 integrated on exemplary CMOS wafer 3102, etc.) canfurther comprise a PMUT array, as described herein, comprising the MUTstructure (e.g., exemplary PMUT 2700 or portions thereof, exemplary PMUT3000 or portions thereof, etc.) in an array of MUT structures (e.g.,exemplary PMUT arrays (2902, 2904, 2906), etc.), wherein the MUTstructure in the array of MUT structures are configured in a rhombusconfiguration (2908), in a hexagonal configuration (2912), and/or anycombination thereof (e.g., exemplary PMUT arrays 2906). As anon-limiting example, an exemplary MUT structure (e.g., exemplary PMUT2700 or portions thereof, exemplary PMUT 3000 or portions thereof, etc.)and the array of MUT structures (e.g., exemplary PMUT arrays 2906, etc.)can comprise a first two of the array of MUT structures in the rhombusconfiguration 2910 and a second two of the array of MUT structures inthe hexagonal configuration 2914 arranged as a unit cell (e.g.,exemplary PMUT arrays 2906, etc.).

In addition, in further non-limiting embodiments of the subjectdisclosure can comprise an exemplary MEMS device (e.g., exemplary PMUT3000 integrated on exemplary CMOS wafer 3102, etc.), comprising a CMOSdevice wafer (e.g., exemplary CMOS wafer 3102) associated with a PMUTarray of a fingerprint sensor and having a plurality of cavities (e.g.,cavities 3202) configured in an array.

In a non-limiting aspect, exemplary MEMS device (e.g., exemplary PMUT3000 integrated on exemplary CMOS wafer 3102, etc.) can further comprisea first metal conductive layer (e.g., such as described regarding one ormore exemplary top electrodes 4402, etc., in reference to FIG. 44)disposed on the CMOS device wafer (e.g., exemplary CMOS wafer 3102) andover the plurality of cavities (e.g., cavities 3202).

In another non-limiting aspect, exemplary MEMS device (e.g., exemplaryPMUT 3000 integrated on exemplary CMOS wafer 3102, etc.) can furthercomprise a piezoelectric material (e.g., one or more of scandium dopedaluminum nitride, scandium doped aluminum nitride of about 10-30%,scandium doped aluminum nitride of greater than about 30%) disposed onthe first metal conductive layer (e.g., such as described regarding oneor more exemplary top electrodes 4402, etc., in reference to FIG. 44).In still another non-limiting aspect, exemplary MEMS device (e.g.,exemplary PMUT 3000 integrated on exemplary CMOS wafer 3102, etc.) canfurther comprise one or more bottom electrodes (e.g., one or moreexemplary bottom contacts 4002, etc.) electrically coupled to one ormore top electrodes (e.g., one or more exemplary top electrodes 4402,etc.) via the piezoelectric material. In addition, further non-limitingembodiments of exemplary MEMS device (e.g., exemplary PMUT 3000integrated on exemplary CMOS wafer 3102, etc.) can further comprise anacoustic propagation layer over the one or more top electrodes (e.g.,one or more exemplary top electrodes 4402, etc.), for example, asfurther described above, for example, regarding FIG. 18. As anon-limiting example, an exemplary acoustic propagation layer comprisinga liquid, a polymer, or an acoustic impedance matching materialconfigured to provide acoustic impedance matching between a PMUT deviceassociated with the one or more top electrodes and the cover layer, canbe deposited over the one or more top electrodes (e.g., one or moreexemplary top electrodes 4402, etc.).

In a further non-limiting aspect, exemplary MEMS device (e.g., exemplaryPMUT 3000 integrated on exemplary CMOS wafer 3102, etc.) can furthercomprise a second metal conductive layer (e.g., molybdenum (Mo) layer3806, etc.), disposed on the piezoelectric material (e.g., one or moreof scandium doped aluminum nitride, scandium doped aluminum nitride ofabout 10-30%, scandium doped aluminum nitride of greater than about30%), electrically coupling the second metal conductive layer and one ormore CMOS device wafer electrode (e.g., associated with exemplary topmetal layer 3112), and electrically coupling the first metal conductivelayer (e.g., such as described regarding one or more exemplary topelectrodes 4402, etc., in reference to FIG. 44) to one or more otherCMOS device wafer electrode (e.g., associated with exemplary top metallayer 3112), wherein the plurality of cavities (e.g., cavities 3202),the piezoelectric material, the first metal conductive layer, and thesecond metal conductive layer are configured as a plurality of PMUTstructures (e.g., a plurality of exemplary PMUTs 3000, or portionsthereof, integrated on exemplary CMOS wafer 3102, etc.).

As a non-limiting example, the plurality of PMUT structures (e.g., aplurality of exemplary PMUTs 3000, or portions thereof, integrated onexemplary CMOS wafer 3102, etc.) can be formed integrally to a CMOSstructure (e.g., exemplary CMOS wafer 3102, or portions thereof, etc.),and wherein the fingerprint sensor is adapted to sense a characteristicof a fingerprint placed adjacent to the PMUT array and opposite theplurality of cavities (e.g., cavities 3202). In a further non-limitingexample, the plurality of PMUT structures (e.g., a plurality ofexemplary PMUTs 3000, or portions thereof, integrated on exemplary CMOSwafer 3102, etc.) can comprise the plurality of PMUT structures in arhombus configuration (2908), in a hexagonal configuration (2912),and/or in any combination thereof (e.g., exemplary PMUT arrays 2906). Asa non-limiting example, an exemplary PMUT structure (e.g., exemplaryPMUT 3000 or portions thereof, etc.) and the plurality of PMUTstructures (e.g., exemplary PMUT arrays 2906, etc.) can comprise a firsttwo of the plurality of PMUT structures in the rhombus configuration2910 and a second two of the plurality of MUT structures in thehexagonal configuration 2914 arranged as a unit cell (e.g., exemplaryPMUT arrays 2906, etc.).

In view of the subject matter described supra, methods that can beimplemented in accordance with the subject disclosure will be betterappreciated with reference to the flowcharts of FIGS. 46-47. While forpurposes of simplicity of explanation, the methods are shown anddescribed as a series of blocks, it is to be understood and appreciatedthat such illustrations or corresponding descriptions are not limited bythe order of the blocks, as some blocks may occur in different ordersand/or concurrently with other blocks from what is depicted anddescribed herein. Any non-sequential, or branched, flow illustrated viaa flowchart should be understood to indicate that various otherbranches, flow paths, and orders of the blocks, can be implemented whichachieve the same or a similar result. Moreover, not all illustratedblocks may be required to implement the methods described hereinafter.

FIG. 46 depicts an exemplary flowchart of non-limiting methods 4600associated with a various non-limiting embodiments of the subjectdisclosure. For instance, exemplary methods 4600 can comprise, at 4602,forming a plurality of cavities (e.g., cavities 3202) in a CMOS devicewafer (e.g., exemplary CMOS wafer 3102). As a non-limiting example,forming the plurality of cavities at 4602 can comprise forming a PMUT(e.g., exemplary PMUT 3000 integrated on exemplary CMOS wafer 3102,etc.) array of a fingerprint sensor adapted to sense a characteristic ofa fingerprint placed adjacent to the PMUT array and opposite theplurality of cavities (e.g. cavities 3202). In a further non-limitingexample, forming the PMUT array comprises forming a plurality of PMUTdevices in a rhombus configuration (2908), in a hexagonal configuration(2912), and/or in any combination thereof (e.g., exemplary PMUT arrays2906), for example, as further described above regarding FIG. 29. In yetanother non-limiting example, exemplary methods 4600 can furthercomprise forming a first two of the plurality of PMUT devices (e.g.,exemplary PMUT 3000 integrated on exemplary CMOS wafer 3102, etc.) inthe rhombus configuration 2910 and a second two of the plurality of PMUTdevices (e.g., exemplary PMUT 3000 integrated on exemplary CMOS wafer3102, etc.) in the hexagonal configuration 2914 arranged as a unit cell(e.g., exemplary PMUT arrays 2906, etc.).

Exemplary methods 4600 can further comprise, at 4604, depositing andpatterning a piezoelectric layer (e.g., comprising aluminum nitride,lead zirconate titanate (PZT), zinc oxide, polyvinylidene difluoride(PVDF), lithium niobate (LiNbO3), etc.) over the plurality of cavities(e.g., cavities 3202). Alternatively, exemplary methods 4600 can furthercomprise, at 4604, depositing and patterning a piezoelectric layer(e.g., one or more of scandium doped aluminum nitride, scandium dopedaluminum nitride of about 10-30%, scandium doped aluminum nitride ofgreater than about 30%) over the plurality of cavities (e.g., cavities3202). In addition, exemplary methods 4600 can comprise, at 4606,forming a plurality of openings in the piezoelectric layer (e.g.,comprising aluminum nitride, scandium doped aluminum nitride, leadzirconate titanate (PZT), zinc oxide, polyvinylidene difluoride (PVDF),lithium niobate (LiNbO3), etc.) over the plurality of cavities (e.g.,cavities 3202) to expose a first conductive material layer (e.g.,molybdenum (Mo) layer 3806, etc.) under the piezoelectric layer and toexpose at least one CMOS device wafer (e.g., exemplary CMOS wafer 3102)electrode (e.g., associated with exemplary top metal layer 3112).

In addition, exemplary methods 4600, at 4608, can further comprisedepositing and patterning a second conductive material layer (e.g., suchas described regarding one or more exemplary top electrodes 4402, etc.,in reference to FIG. 44) over the piezoelectric layer (e.g., comprisingaluminum nitride, scandium doped aluminum nitride, lead zirconatetitanate (PZT), zinc oxide, polyvinylidene difluoride (PVDF), lithiumniobate (LiNbO3), etc.) to establish an electrical connection betweenthe one or more CMOS device wafer (e.g., exemplary CMOS wafer 3102)electrode (e.g., associated with exemplary top metal layer 3112) and thesecond conductive material layer. As a non-limiting example, exemplarymethods 4600 can further comprise, at 4608, forming one or more bottomelectrodes (e.g., one or more exemplary bottom contacts 4002, etc.)electrically coupled to one or more top electrodes (e.g., one or moreexemplary top electrodes 4402, etc.) via the piezoelectric layer.

Exemplary methods 4600, at 4610, can further comprise depositing anacoustic propagation layer over the one or more top electrodes (e.g.,one or more exemplary top electrodes 4402, etc.), for example, asfurther described above, for example, regarding FIG. 18. As anon-limiting example, an exemplary acoustic propagation layer comprisinga liquid, a polymer, or an acoustic impedance matching materialconfigured to provide acoustic impedance matching between a PMUT device(e.g., exemplary PMUT 3000 integrated on exemplary CMOS wafer 3102,etc.) associated with the one or more top electrodes and the coverlayer, can be deposited over the one or more top electrodes (e.g., oneor more exemplary top electrodes 4402, etc.), for example, as describedabove regarding FIG. 18. In addition, exemplary methods 4600, at 4612,can further comprise depositing a cover layer over the acousticpropagation layer, to facilitate providing further protection to thePMUT device (e.g., exemplary PMUT 3000 integrated on exemplary CMOSwafer 3102, etc.) from debris, contaminants, etc. from introducingerrors in measurements associated with PMUT device (e.g., exemplary PMUT3000 integrated on exemplary CMOS wafer 3102, etc.).

FIG. 47 depicts another exemplary flowchart of non-limiting methodsassociated with a various non-limiting embodiments of the subjectdisclosure. For instance, exemplary methods 4700, can comprise forming aplurality of cavities (e.g., cavities 3202) in a CMOS device wafer(e.g., exemplary CMOS wafer 3102). As a non-limiting example, exemplarymethods 4700, at 4702, can comprise filling the plurality of cavities(e.g., cavities 3202) in the CMOS device wafer (e.g., exemplary CMOSwafer 3102) with sacrificial material (e.g., one or more exemplarysacrificial materials 3302, amorphous silicon, etc.). In a furthernon-limiting example, exemplary methods 4700, at 4704, can compriseplanarizing the sacrificial material (e.g., one or more exemplarysacrificial materials 3302, amorphous silicon, etc.) on the CMOS devicewafer (e.g., exemplary CMOS wafer 3102), and at 4706, can furthercomprise depositing a capping layer (e.g., one or more exemplary silicondioxide (SiO₂) layers 3402, etc.) over the sacrificial material (e.g.,one or more exemplary sacrificial materials 3302, amorphous silicon,etc.).

Exemplary methods 4700, at 4708, can further comprise forming one ormore openings (e.g., one or more exemplary seal holes 3502) in thecapping layer (e.g., one or more exemplary silicon dioxide (SiO₂) layers3402, etc.) to expose the sacrificial material (e.g., one or moreexemplary sacrificial materials 3302, amorphous silicon, etc.), and at4710, can further comprise selectively removing the sacrificialmaterial. In addition, exemplary methods 4700, at 4712, can furthercomprise sealing the one or more openings in the capping layer (e.g.,one or more exemplary silicon dioxide (SiO₂) layers 3402, etc.), inaddition to depositing the first conductive material layer (e.g.,molybdenum (Mo) layer 3806, etc.) comprising a metal conductive layerover the capping layer (e.g., one or more exemplary silicon dioxide(SiO₂) layers 3402, etc.).

As used in this application, the term “or” is intended to mean aninclusive “or” rather than an exclusive “or”. That is, unless specifiedotherwise, or clear from context, “X employs A or B” is intended to meanany of the natural inclusive permutations. That is, if X employs A; Xemploys B; or X employs both A and B, then “X employs A or B” issatisfied under any of the foregoing instances. In addition, thearticles “a” and “an” as used in this application and the appendedclaims should generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. In addition, the word “coupled” is used herein to mean direct orindirect electrical or mechanical coupling. In addition, the words“example” and/or “exemplary” are used herein to mean serving as anexample, instance, or illustration. Any aspect or design describedherein as “example” and/or “exemplary” is not necessarily to beconstrued as preferred or advantageous over other aspects or designs.Rather, use of the word exemplary is intended to present concepts in aconcrete fashion.

What has been described above includes examples of the subjectdisclosure. It is, of course, not possible to describe every conceivablecombination of components or methodologies for purposes of describingthe subject matter, but it is to be appreciated that many furthercombinations and permutations of the subject disclosure are possible.Accordingly, the claimed subject matter is intended to embrace all suchalterations, modifications, and variations that fall within the spiritand scope of the appended claims.

In particular and in regard to the various functions performed by theabove described components, devices, systems and the like, the terms(including a reference to a “means”) used to describe such componentsare intended to correspond, unless otherwise indicated, to any componentwhich performs the specified function of the described component (e.g.,a functional equivalent), even though not structurally equivalent to thedisclosed structure, which performs the function in the hereinillustrated exemplary aspects of the claimed subject matter.

The aforementioned systems have been described with respect tointeraction between several components. It can be appreciated that suchsystems and/or components can include those components or specifiedsub-components, some of the specified components or sub-components,and/or additional components, and according to various permutations andcombinations of the foregoing. Sub-components can also be implemented ascomponents communicatively coupled to other components rather thanincluded within parent components (hierarchical). Additionally, itshould be noted that one or more components may be combined into asingle component providing aggregate functionality or divided intoseveral separate sub-components, and any one or more middle layers, maybe provided to communicatively couple to such sub-components in order toprovide integrated functionality. Any components described herein mayalso interact with one or more other components not specificallydescribed herein.

In addition, while a particular feature of the subject disclosure mayhave been disclosed with respect to only one of several implementations,such feature may be combined with one or more other features of theother implementations as may be desired and advantageous for any givenor particular application. Furthermore, to the extent that the terms“includes,” “including,” “has,” “contains,” variants thereof, and othersimilar words are used in either the detailed description or the claims,these terms are intended to be inclusive in a manner similar to the term“comprising” as an open transition word without precluding anyadditional or other elements.

Reference throughout this specification to “one embodiment,” or “anembodiment,” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrase “in oneembodiment,” or “in an embodiment,” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments.

In this regard, while the disclosed subject matter has been described inconnection with various embodiments and corresponding figures, whereapplicable, it is to be understood that other similar embodiments can beused or modifications and additions can be made to the describedembodiments for performing the same, similar, alternative, or substitutefunction of the disclosed subject matter without deviating therefrom.Therefore, the disclosed subject matter should not be limited to anysingle embodiment described herein, but rather should be construed inbreadth and scope in accordance with the appended claims below.

What is claimed is:
 1. A microelectromechanical systems (MEMS) device,comprising: a MEMS ultrasound transducer (MUT) structure and apiezoelectric material comprising scandium disposed within the MEMSdevice comprising a piezoelectric MUT (PMUT) array of a fingerprintsensor adapted to sense a characteristic of a fingerprint placedadjacent to the MUT structure; a first metal conductive layer disposedon the piezoelectric material; and a plurality of metal electrodesconfigured to form electrical connections between the first metalconductive layer, the piezoelectric material, and a complementary metaloxide semiconductor (CMOS) structure, wherein the pMUT structure and theCMOS structure are vertically stacked, wherein the PMUT array comprisesthe MUT structure in an array of MUT structures, and wherein the MUTstructure and the array of MUT structures comprise a first two of thearray of MUT structures in the rhombus configuration and a second two ofthe array of MUT structures in the hexagonal configuration arranged as aunit cell.
 2. The MEMS device of claim 1, further comprising: a secondmetal conductive layer disposed on the piezoelectric material andopposite the first metal conductive layer.
 3. The MEMS device of claim1, further comprising: a stand-off formed on the piezoelectric material.4. The MEMS device of claim 3, wherein the stand-off comprises a silicondioxide layer deposited over the piezoelectric material.
 5. The MEMSdevice of claim 3, wherein the MUT structure is bonded to the CMOSstructure at the standoff via at least one of a eutectic bonding layer,a compression bond, or a conductive epoxy.
 6. The MEMS device of claim5, wherein the eutectic bonding layer comprises an aluminum-germaniumeutectic bonding layer.
 7. The MEMS device of claim 5, wherein the MUTstructure is electrically coupled to the CMOS structure at the standoff.8. The MEMS device of claim 1, wherein the piezoelectric materialcomprises scandium doped aluminum nitride.
 9. The MEMS device of claim1, further comprising: a piezoelectric layer comprising an aluminumnitride (AlN) seed layer, a bottom metal layer, and an aluminum nitride(AlN) layer.